EP3804553A1 - Schliff für einen edelstein - Google Patents

Schliff für einen edelstein Download PDF

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Publication number
EP3804553A1
EP3804553A1 EP19202573.2A EP19202573A EP3804553A1 EP 3804553 A1 EP3804553 A1 EP 3804553A1 EP 19202573 A EP19202573 A EP 19202573A EP 3804553 A1 EP3804553 A1 EP 3804553A1
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EP
European Patent Office
Prior art keywords
facets
crown
gemstone
girdle
main
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP19202573.2A
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English (en)
French (fr)
Inventor
Günther Blasbichler
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D Swarovski KG
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D Swarovski KG
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Publication date
Application filed by D Swarovski KG filed Critical D Swarovski KG
Priority to EP19202573.2A priority Critical patent/EP3804553A1/de
Publication of EP3804553A1 publication Critical patent/EP3804553A1/de
Withdrawn legal-status Critical Current

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    • A—HUMAN NECESSITIES
    • A44—HABERDASHERY; JEWELLERY
    • A44C—PERSONAL ADORNMENTS, e.g. JEWELLERY; COINS
    • A44C17/00—Gems or the like
    • A44C17/001—Faceting gems
    • A—HUMAN NECESSITIES
    • A44—HABERDASHERY; JEWELLERY
    • A44C—PERSONAL ADORNMENTS, e.g. JEWELLERY; COINS
    • A44C17/00—Gems or the like
    • A44C17/007—Special types of gems
    • A44C17/008—Glass stones

Definitions

  • the invention relates to a cut for a gemstone, and in particular to a cut for a flat back gemstone.
  • Articles comprising the gemstone and methods for improving the optical properties of a gemstone are also provided.
  • Faceted gemstones have been used to embellish products for a long time.
  • the optical properties of gemstones are particularly important characteristics in this context, and these properties are defined at least in part by the geometry of the gemstone.
  • the optical properties of a gemstone are often compared to those of a gemstone with a brilliant cut.
  • the brilliant cut is a complex geometry with four different types of crown facets (including a table) and two different types of pavilion facets, all of which interact to create advantageous optical properties such as brilliance.
  • Such components can be combined with a mirrored surface on the flat back in order to create a "sparkling effect" where light incident on the mirror surface is reflected in multiple directions due to the interaction with the facets of the component.
  • flat backed gemstones typically have inferior optical properties compared to e.g. a brilliant cut, due to the absence of pavilion facets, even in the presence of a reflective layer.
  • the invention resides in a gemstone comprising a crown and a girdle at which the gemstone has its largest transverse dimension, the crown comprising a first set of main crown facets inclined relative to the plane of the girdle and adjoining each other around the perimeter of the crown, wherein the crown further comprises a second set of crown facets meeting at an apex of the crown.
  • the second set of crown facets can be considered to define the apex of the gemstone.
  • the invention resides in a gemstone comprising a crown and a girdle at which the gemstone has its largest transverse dimension, the crown comprising first and second sets of main crown facets inclined relative to the plane of the girdle and alternating around the perimeter of the crown, wherein the crown further comprises a third set of crown facets meeting at an apex of the crown, while two sets of main crown facets (the 'first' and 'third' crown facets) alternate around the perimeter of the crown.
  • the term 'alternate' it is meant that one first main crown facet is directly adjacent one third (main) crown facet and this relationship repeats around the perimeter of the crown; i.e. each third (main) crown facet is located between adjacent pairs of first main crown facets and vice versa.
  • the present inventors have surprisingly discovered that the inclusion of a set of crown facets meeting at / defining an apex of the crown (termed herein the 'second set' of crown facets), instead of a table (which is common in the art), results in a gemstone with particularly advantageous brilliance properties. These advantages are particularly salient when the gemstone has a substantially flat back.
  • the second set of crown facets is spaced from the girdle by the first and third sets of main crown facets.
  • the second set of crown facets is spaced from the girdle by the first set of main crown facets.
  • the apex is an apex in the strict geometric sense of the word, or the apex may comprise a small flat or slightly rounded region ('culet').
  • the small flat or slightly rounded region of the apex represents less than 5%, less than 4%, less than 3%, less than 2% or less than 1% of the surface area of the gemstone when viewed from above.
  • all facets in a set are substantially identical.
  • facets may be considered to be identical if they have substantially the same shape and are arranged at substantially the same angle relative to the plane of the girdle. In asymmetric embodiments of the invention, however, facets of one type may vary in shape as discussed herein below.
  • the plane of the girdle is an imaginary plane relative to which all of the facets within a set of facets typically have the same orientation and distance.
  • gemstone embodiments of any aspect of the invention comprise a substantially flat back.
  • a reflective layer is provided on the substantially flat back to reflect light incident on the reflective layer through the facets of the crown.
  • the flat back is substantially parallel to the plane of the girdle.
  • the present configuration of the crown of a gemstone according to the invention is particularly beneficial in the context of gemstones with a flat back, where the light return and fire may be relatively low due to a lack of pavilion facets.
  • the gemstone may comprise a shallow pavilion.
  • the gemstone may comprise a pavilion that has shorter height than the crown: for example, at least twice as short as the crown, and preferably at most about 20%, or at most about 10% of the height of the crown.
  • the girdle has a height of no more than about 33% of the height of the crown, no more than about 25% of the height of the crown, no more than about 20% of the height of the crown, or no more than about 15% of the height of the crown.
  • the girdle (when present) has a height of no more than about 15% of the diameter of the gemstone and preferably no more than 10% of the diameter of the gemstone.
  • the girdle is substantially circular. Circular gemstones are commonly used for their optically pleasing symmetry.
  • the facets in the second set of crown facets adjoin the facets of the third set of (main) crown facets. In embodiments of the first aspect, the facets in the second set of crown facets adjoin the facets of the first set of main crown facets.
  • the facets in the first set of main crown facets adjoin the girdle with a broad side.
  • the facets in the third set of main crown facets (which alternate around the circumference of the girdle with the facets of the first set of main crown facets) adjoin the girdle with a point.
  • the facets in the second set of crown facets are substantially kite-shaped. In some such embodiments, the facets of the second set of crown facets adjoin each other with their long sides.
  • kite-shaped is intended to define a quadrilateral whose four sides can be grouped into two pairs of substantially equal-length sides (a pair of relatively short 'minor' sides and a pair of relatively long 'major' sides) that are adjacent to each other.
  • adjacent sides of a facet may, intentionally or inadvertently, not meet at a perfect vertex.
  • the respective facet(s) may comprise one or more additional short side separating the pair of adjacent longer facet sides.
  • the short side is typically significantly shorter than the adjoining longer sides, and may for example have a length of between 0 and about 10%, between 0 and about 5%, or between 0 and about 2% of the length of the adjacent longer sides.
  • a facet may be considered to be substantially kite-shaped if it has four main sides (a pair of relatively short main sides, i.e. 'minor' sides, and a pair of relatively long main sides, i.e. 'major' sides), and optionally one or more small / short sides between main sides, the small sides being significantly shorter than the main sides (such as e.g. below about 10%, preferably below about 5% of the length of the adjoining main sides).
  • the facets in the second set of crown facets may comprise an additional short side between the long, major sides.
  • the short side is preferably significantly shorter than the adjoining major (long) sides L 150 , and may for example have a length of between 0 and about 10%, between 0 and about 5%, or between 0 and about 2% of the length of the major sides L 150 .
  • the facets in the second set of crown facets may comprise an additional short side between the short, minor sides.
  • the additional short side is preferably significantly shorter than the adjoining minor sides S 150 , and may for example have a length of between 0 and about 10%, between 0 and about 5%, or between 0 and about 2% of the length of the minor sides S 150 .
  • one or more of the facets in the third set of crown facets may comprise an additional short side between the short / minor sides. This may occur, for example, due to small errors in the location of the facets of the first and second sets of crown facets such that some facets in the first set of crown facets do not adjoin the facets of the third set of crown facets at a perfect triangular tip.
  • the facets of the third set of crown facets may be pentagonal or hexagonal, with four main sides (comprising two major sides and two minor sides) and one or two small / short sides between pairs of main sides.
  • the facets in the third set of main crown facets are substantially kite-shaped.
  • the facets of the third set of main crown facets adjoin the facets of the first set of main crown facets at their long sides.
  • the facets in the second set of crown facets and the facets in the third set of main crown facets are substantially kite-shaped.
  • the facets in the second set of crown facets adjoin the facets of the third set of main crown facets with their respective short sides.
  • the facets in the first set of main crown facets are substantially triangular. In some embodiments of the first aspect, the facets in the first set of main crown facets are substantially pentagonal. In embodiments, the side of the triangle / pentagon that adjoins the girdle may be curved. As discussed with respect to other facets above, in some embodiments, one or more of the facets in the first set of main crown facets is / are triangular / pentagonal with a small flat tip at the apex of the triangle or pentagon that is furthest from the girdle.
  • an additional small / short side may be present between the main sides of the facets that extend away from the girdle, where the additional small side has preferably at most about 10%, at most about 5% or at most about 2% of the length of the adjoining main sides of the facet.
  • the first and third sets of main crown facets suitably alternate around the perimeter of the crown such that the number of facets in the first set of main crown facets is equal to the number of facets in the third set of main crown facets.
  • the number of facets in the second set of crown facets may be equal to the number of facets in the first or third set of main crown facets.
  • the number of facets in the second set of crown facets may be equal to the number of facets in the first set of main crown facets.
  • the facets in the second set of crown facets are arranged at azimuthal angles that are the arithmetic average of the azimuthal angles at which adjoining facets in the third set of main crown facets are arranged.
  • the facets in the second set of crown facets are arranged at azimuthal angles that are the arithmetic average of the azimuthal angles at which adjoining facets in the first set of main crown facets are arranged.
  • the number of facets in the first or third (where present) set of main crown facets is 6, 7, 8 or 9. In some embodiments, the number of facets in the second set of crown facets is equal to 6, 7, 8 or 9; or may be 12, 14, 16 or 18. In embodiments, the crown facets of the gemstone have 6, 7, 8 or 9-fold symmetry. In some embodiments, the crown facets have 7-fold symmetry.
  • the number of facets in each set of the first and third set of main crown facets is 7.
  • the use of 7-fold symmetry / 7 facets in the first and third sets of main crown facets has been shown to result in particularly high fire values. In such embodiments the number of facets in the second set of crown facets may be 7 or 14; preferably 7.
  • all of the facets of the crown belong to the first set of main crown facets, the second set of crown facets and the third set of main crown facets (if present).
  • the angle between the facets of the second set of crown facets and the plane of the girdle is smaller than both (i) the angle between the facets of the first set of main crown facets and the plane of the girdle, and (ii) the angle between the facets of the third set of (main) crown facets and the plane of the girdle.
  • the angle between the facets of the second set of crown facets and the plane of the girdle is smaller than the angle between the facets of the first set of main crown facets and the plane of the girdle.
  • the use of a smaller (shallower) angle for the facets in the second set of crown facets also advantageously reduces the risks of damage to the apex of the crown and improves the ease of manipulation and application of the gemstone onto surfaces such as e.g. the surface of articles onto which the gemstones are to be applied.
  • the angle between the facets of the first type of main crown facets and the plane of the girdle is larger than the angle between the facets of the third set of (main) crown facets and the plane of the girdle.
  • the angle between the facets of the first set of main crown facets and the plane of the girdle may be at most about 43°. In embodiments of any aspect, the angle between the facets of the first set of main crown facets and the plane of the girdle may be at least 38°. Thus, in some embodiments of any aspect, the angle between the facets of the first set of main crown facets and the plane of the girdle may be in the range of between about 38° and about 43°.
  • the angle between the facets of the first set of main crown facets and the plane of the girdle is in the range of 40.4° ⁇ 6°, 40.4° ⁇ 3°, 40.4° ⁇ 1.5° or 40.4° ⁇ 0.75°.
  • the angle between the facets of the first set of main crown facets and the plane of the girdle is in the range of 42.20° ⁇ 6°, 42.20° ⁇ 3°, 42.20° ⁇ 1.5° or 42.20° ⁇ 0.75°.
  • the angle between the facets of the second set of crown facets and the plane of the girdle may be at most about 26°. In embodiments, the angle between the facets of the second set of crown facets and the plane of the girdle may be at least 12°. Thus, in some embodiments of any aspect, the angle between the facets of the second set of main crown facets and the plane of the girdle may be in the range of between about 12° and about 26° or between about 16° and about 21°.
  • the angle between the facets of the second set of crown facets and the plane of the girdle is in the range of 18.2° ⁇ 6°, 18.2° ⁇ 3°, 18.2° ⁇ 1.5°, or 18.2° ⁇ 0.75°.
  • the angle between the facets of the second set of crown facets and the plane of the girdle is in the range of 19.2° ⁇ 6°, 19.2° ⁇ 3°, 19.2° ⁇ 1.5°, or 19.2° ⁇ 0.75°. In some particular embodiments of the second aspect, the angle between the facets of the second set of crown facets and the plane of the girdle is in the range of 19.16° ⁇ 0.75°.
  • the angle between the facets of the third set of (main) crown facets and the plane of the girdle is in the range of 36.1° ⁇ 6°; or in the range of 36.1° ⁇ 3°; or in the range of 36.1° ⁇ 1.5°; or in the range of 36.1° ⁇ 0.75°.
  • the angle between the facets of the first set of main crown facets and the plane of the girdle is between about 38° and about 43°
  • the angle between the facets of the third set of (main) crown facets and the plane of the girdle is between about 33° and about 38°
  • the angle between the facets of the second set of crown facets and the plane of the girdle is between about 12° and about 26°.
  • the angle between the facets of the first set of main crown facets and the plane of the girdle may be in the range 42.20° ⁇ 0.75°
  • the angle between the facets of the third set of (main) crown facets and the plane of the girdle may be in the range 36.1° ⁇ 0.75°
  • the angle between the facets of the second set of crown facets and the plane of the girdle may be in the range 19.2° ⁇ 0.75° or 19.16° ⁇ 0.75°.
  • a method of improving the optical properties of a gemstone having a flat back comprising cutting a gemstone to provide first set of main crown facets inclined relative to the plane of the girdle around the perimeter of the crown, and a second set of crown facets meeting at an apex of the crown and spaced from the girdle by the facets of the first set of main crown facets.
  • a method of improving the optical properties of a gemstone having a flat back comprising cutting a gemstone to provide first and third sets of main crown facets inclined relative to the plane of the girdle and alternating around the perimeter of the crown, and a second set of crown facets meeting at an apex of the crown.
  • the facets of the second set of crown facets are spaced from the girdle by the facets of the first and third sets of main crown facets.
  • Embodiments of the third and fourth aspects of the invention may comprise any of the features of the first and second aspects, respectively.
  • any of the features of the gemstone, any coatings or layers applied thereon and described in relation to the first aspect apply equally to the gemstone of the second aspect.
  • the invention provides an article comprising a gemstone according to the invention.
  • the article is a decorative article.
  • Embodiments of this aspect may comprise a gemstone having any of the features of the gemstone of the first or second aspect.
  • any of the aspects of the invention may comprise any of the features described in relation to any other aspect of the invention, unless such features are clearly not compatible.
  • any of the features of any embodiment of the invention for example, the embodiments of the first and second aspects of the invention described above - are (where not obviously incompatible), intended and envisaged to be combined in any and all combinations; and all such combinations are hereby encompassed.
  • any one or more optional feature of the first set of crown facets are intended to be combined with any one or more optional features of the second set of crown facets and any one or more optional features of the third set of crown facets (where present); and any such resulting gemstone is considered to represent a gemstone according to the invention.
  • a gemstone with superior optical properties could be obtained by providing either two or three sets of crown facets: a first set of main crown facets and a second set of crown facets that meet at an apex of the crown; in some aspect and embodiments comprising a third set of (main) crown facets that alternate around the perimeter of the crown with the first set of main crown facets.
  • the second set of crown facets is spaced from the pavilion by the first and, in some embodiments, the third sets of main crown facets.
  • the terms 'back' / 'bottom', and 'front' / 'top' surface are used to refer to the surfaces of a gemstone that when incorporated in an article (such as e.g. when applied to the surface of an article), are intended to face towards a viewer (front / top surface) or away from a viewer, such as towards the surface on which the gemstone is applied or supported (back / bottom surface), respectively.
  • gemstones may have a complex geometry, as required by the circumstances, and as such a back or front surface may, in fact, comprise a collection of jointed or disjointed surfaces.
  • a front surface is intended to be visible in use, whereas a back surface is generally intended to be attached to or otherwise combined with an article.
  • FIGs 1A, 1B and 1C show schematic top ( Figure 1A ), bottom ( Figure 1B ) and side ( Figure 1C ) views of a brilliant cut gemstone 1 according to the prior art.
  • the gemstone 1 comprises a crown 2, a pavilion 6, and a girdle 4.
  • the crown 2 forms the top (or 'front') part of the gemstone 1.
  • the crown comprises a large flat facet 12 called the 'table' which is parallel to the plane of the girdle 4, and three types of crown facets 8, 10, 14 provided between the table 12 and the girdle 4.
  • Facets 8 are commonly referred to as 'bezel facets'.
  • Facets 10 are commonly referred to as 'star facets'.
  • Facets 14 are commonly referred to as 'upper half facets'.
  • the gemstone illustrated on Figures 1A to 1C has an 8-fold symmetry in both the crown 2 and the pavilion 6.
  • the crown comprises an octagonal table 12, eight star facets 10, eight bezel facets 8, and sixteen upper half facets 14. Pairs of upper half facets 14 alternate with single bezel facets 8 around the upper perimeter of the pavilion 6.
  • the pavilion 6 forms the bottom (or 'back' or 'lower') part of the gemstone 1.
  • the pavilion 6 comprises two types of facets.
  • a first set of pavilion facets 16 is commonly referred to as 'pavilion main facets' and meet at an apex 20.
  • the apex 20 may be an apex in the strict geometric sense of the word, or may be in the form of a small flat facet referred to as a 'culet'.
  • the culet 20, when present, is typically significantly smaller than the other pavilion facets.
  • a second set of pavilion facets 18 is commonly referred to as 'lower half facets'.
  • the pavilion 6 comprises eight pavilion main facets 16 and sixteen lower half facets 18. Pairs of lower half facets 18 alternate with single pavilion main facets 16 around the lower perimeter of the pavilion 6.
  • the girdle 4 is the region that forms the junction between the crown 2, and the pavilion 6, if present. As such, the girdle 4 is the region at which the gemstone has its largest transverse dimension.
  • the girdle is associated with an imaginary plane P G , referred to as the 'plane of the girdle' or 'girdle plane', illustrated by the dashed line on Figure 1C .
  • the plane P G is arranged such that all of the crown facets (and all of the pavilion facets, if present) within a set of facets have the same orientation and distance to the plane P G , when taking into account symmetries in the set.
  • the upper half facets 14 are provided in pairs where each pair comprises facets that mirror each other.
  • a 'set' or 'type' of facets refers to a group of facets that are substantially identical in shape, and that have the same or symmetrical orientations relative to the girdle plane P G .
  • the light return is the extent of internal and external reflections of 'white' light seen in a polished gemstone when viewed face up.
  • the scintillation is the appearance of spots of light seen in a polished gemstone when viewed face up that flash as the gemstone, observer, or light source moves (also referred to as 'sparkle'); and the relative size, arrangement, and contrast of bright and dark areas seen in a polished gemstone when viewed face up while that gemstone is still or moving (also referred to as 'pattern').
  • the system for measuring parameters of a gemstone as illustrated in Figure 2A provides a light source around a hemisphere H centred on the gemstone 1 and extending from the girdle plane P G of the gemstone 1 under evaluation, and evaluates the influence of light coming from different angles around the hemisphere H on light reflections seen by an observer O of the gemstone from the front / top centre of the gemstone (i.e. perpendicular to the girdle plane P G , through the table 12 of the gemstone if present).
  • the hemisphere H is divided into three distinct segments 22, 24, 26, and the light reflections caused by illumination of these segments are separately evaluated; specifically, the hemisphere H is divided into a segment 26 of shallow-angle light, a segment 24 of intermediate angle light, and a segment of steep angle light 22.
  • the pattern of reflections caused by light in each of these segments can be represented as separate shallow-angle, intermediate-angle and steep-angle representations 26', 24', 22' (illustrated in Figure 2A ), respectively; and these can be combined into a single representation 28 ( Figure 2B ).
  • an ideal brilliant cut as shown in Figures 1A to 1C should have about 15% of steep-angle light reflection (shown as relatively lighter areas in the pattern 22', relative to the complete surface area of the reflection pattern), which are evenly distributed and preferably display a star-like pattern; and where the steep-angle light reflection pattern does not comprise a large compact light area in the centre (i.e. no large relatively lighter area in the centre of pattern 22').
  • An ideal brilliant cut should also preferably have a high fraction of intermediate-angle light areas (shown as relatively lighter areas in the pattern 24'), and a small fraction of shallow-angle light areas (shown as relatively lighter areas in the pattern 26').
  • An 'Ideal Cut' (Tolkowsky) diamond gemstone with desirable properties such as e.g.
  • the brilliant cut of Figures 1A to 1C may have light return and fire values of about 69% and 50%, respectively for, where fire can be quantified as a percentage of the maximum possible fire (all white light incident on the gemstone is reflected onto a measurement area and the colour saturation of this reflected light is complete); and light return can be quantified as a percentage compared to the light return that would be obtained from a sample of Spectralon® of the same size as the gemstone under evaluation.
  • Figures 3A, 3B, 3C, 3D and 3E show schematic side ( Figure 3A ), top ( Figure 3B ) and top side perspective ( Figure 3C ) views of a first gemstone 100 according to embodiments of the invention, and schematic side ( Figure 3D ) and top ( Figure 3E ) views of a second gemstone 101 according to embodiments of the invention, both with a seven-fold symmetry of the crown facets.
  • the gemstone 100, 101 comprises a crown 120 and a girdle 140.
  • the crown 120 comprises a first set of main crown facets 110 and a third set of (main) crown facets 130. Facets in the first 110 and third 130 sets of main crown facets alternate around the perimeter of the crown 120, and a second set of crown facets 150, which meet at an apex 200.
  • the crown includes a first set of main crown facets 110 and a second set of crown facets 150, which meet at an apex 200.
  • the apex 200 is an apex in the strict geometric sense.
  • the apex 200 may instead comprise a small flat or slightly rounded region, similar to the culet of the pavilion of a known gemstone.
  • the apex 200 comprises a small flat or slightly rounded region, this is typically so small as to be negligible compared to the surface area of the gemstone when viewed from the top (see Figures 3B and 3E ).
  • the small flat / rounded region of apex 200 may represent less than 5%, less than 4%, less than 3%, less than 2% or less than 1% of the surface area of the gemstone when viewed from the top.
  • the facets 110 in the first set of main crown facets adjoin the girdle 140 with a broad side B 110 .
  • the facets 110 in the first set of main crown facets adjoin the facets 150 of the second set of crown facets with edges S 110 .
  • the facets 130 in the third set of (main) crown facets adjoin the girdle 140 with a point, and the facets 150 in the second set of crown facets with edges S 130 .
  • the facets 110 in the first set of main crown facets are substantially triangular, the side adjoining the girdle B 110 being curved and resulting in a gemstone giving a circular impression when seen from the top (see Figures 3B and 3C ).
  • the facets 110 in the first set of main crown facets are substantially pentagonal with a pair of long edges L 110 , a pair of short edges S 110 (equivalent to edges S150 of the second set of crown facets), and a side B 110 adjoining the girdle, the side adjoining the girdle B 110 being curved and resulting in a gemstone giving a circular impression when seen from the top (see Figure 3E ).
  • the side adjoining the girdle B 110 may have a different shape, and for example, may be more or less curved (or even straight) depending at least on the geometry of the girdle 140.
  • One or more of the facets in the first set of main crown facets may be triangular or pentagonal with a small flat tip at the apex of the triangle / pentagon that is furthest from the girdle. For example, this may occur due to slight errors / offsets in the location of the facets 130, such that the tip of a facet 110 does not form a perfect triangle / pentagon. In other words, an additional short / small side may be present between the facet main sides that extend away from the girdle.
  • the additional short / small side is preferably at most about 10%, at most about 5% or at most about 2% of the length of the adjoining main sides of the facet.
  • a deliberate design choice may be made to introduce one or more short / small sides in place of a point or tip of a facet.
  • the facets 150, 150' in the second set of crown facets are substantially kite-shaped.
  • a kite shape can be considered to represent a quadrilateral whose four sides can be grouped into two pairs of equal-length sides (a pair of minor (short) sides and a pair of major (long) sides) that are adjacent to each other.
  • facets 150, 150' comprise a first pair of sides / edges S 150 and a second pair of sides / edges L 150 , edges S 150 being shorter than edges L 150 .
  • the facets 150, 150' of the second set of crown facets adjoin each other with their long sides L 150 and adjoin the facets 130 of the third set of main crown facets (as shown on Figures 3A and 3B ) or the first set of main crown facets 110' (as shown on Figures 3D and 3E ) with their short sides S 150 .
  • the facets 150, 150' may comprise an additional short / small side between the long sides L 150 .
  • the short / small side is preferably significantly shorter than the adjoining major / long sides L 150 , and may for example have a length of between 0 and about 10%, between 0 and about 5%, or between 0 and about 2% of the length of the major / long sides L 150 .
  • One or more of the facets 150, 150' may instead or in addition comprise an additional short / small side between the minor (short) sides S 150 , for example due to small errors in the location of the facets 110, 130 or 110' such that some facets 110, 110' do not adjoin a facet 150, 150' at a perfect vertex / triangular tip.
  • the facets 150, 150' may be pentagonal or hexagonal, with four main sides L 150 , S 150 and one or two short / small sides between pairs of main sides.
  • a facet may be considered to be substantially kite-shaped if it has four main sides (a pair of minor (short) main sides and a pair of major (long) main sides), and optionally one or more short / small sides between main sides, the short / small sides being significantly shorter than the main sides (such as e.g. below about 10%, preferably below about 5% of the length of the adjoining main sides).
  • the facets 130 in the third set of (main) crown facets are also substantially kite-shaped, comprising a pair of minor (short) edges S 130 and a pair of major (long) edges L 130 .
  • the facets 130 of the third set of main crown facets adjoin the facets 110 of the first set of main crown facets with their long sides L 130 .
  • the facets 130 of the third set of main crown facets adjoin the facets 150 of the second set of crown facets with their short sides S 130 .
  • the number of facets 150 in the second set of crown facets is equal to the number of facets in each of the first 110 and third 130 sets of main crown facets.
  • the first 110 and third 130 sets of main crown facets alternate around the perimeter of the crown such that the number of facets in the first set 110 of main crown facets is also equal to the number of facets in the third set 130 of (main) crown facets.
  • the number of facets 150' in the second set of crown facets is equal to the number of facets in the first 110' set of main crown facets.
  • the crown 120 has seven-fold symmetry and comprises seven facets in each of the first and optionally third sets of main crown facets 110, 130, and in the second set of crown facets. In other embodiments, there may be twice the number of facets in the second set of crown facets as in either of the first and third sets of main crown facets.
  • the facets 150 in the second set of crown facets are arranged at azimuthal angles (i.e. angles around the perimeter of the gemstone when seen from the top) that are the arithmetic average of the azimuthal angles at which adjoining facets 130 in the third set of main crown facets (in the embodiment of Figures 3A to 3C ) or adjoining facets 110' in the first set of main crown facets (in the embodiment of Figures 3D to 3E ).
  • the facets 130 in the third set of main crown facets are arranged at azimuthal angles of 0°, 51.43° (360°/7), 102.86°, 154.29°, 205.72°, 257.15°, and 308.58°.
  • the facets 110' in the first set of main crown facets are arranged at azimuthal angles of 0°, 51.43° (360°/7), 102.86°, 154.29°, 205.72°, 257.15°, and 308.58°.
  • the gemstones 100, 101, 102 further comprise a flat back surface 160 in lieu of a pavilion.
  • the flat back surface 160 is parallel to the girdle plane P G of the gemstone 100, 101, 102.
  • the girdle has a height h g , which is the shortest distance between the flat back surface 160 and an edge of a crown facet - in this case the broad side B 110 of the facets 110 in the first set of main crown facets.
  • the height h g of the girdle may be adjusted depending on the circumstances and the size of the gemstone.
  • the height h g of the girdle may be between 0 and about 3 mm; between 0 and about 2 mm, between 0 and about 1 mm, or between 0 and about 0.5 mm.
  • the appropriate height h g of the girdle may of course vary depending on the size of the gemstone.
  • the girdle (when present) has a height of no more than about 33% of the height of the crown, no more than about 25% of the height of the crown, no more than about 20% of the height of the crown, or no more than about 15% of the height of the crown.
  • the girdle (when present) has a height h g of no more than about 15%, and preferably no more than about 10% of the diameter of the gemstone.
  • the back surface may instead be formed as a shallow pavilion.
  • the gemstone may comprise a pavilion that has a shorter depth / height than the height of the crown 120, such as no more than about half the height of the crown, e.g. no more than about 20% of the height of the crown, or no more than about 10% of the height of the crown.
  • the pavilion may have a configuration similar to that shown in Figures 1B and 1C , but with significantly shallower angles.
  • the pavilion (where present) has a symmetry adapted to match the symmetry of the crown (e.g.
  • the symmetry of the pavilion may be different to the symmetry of the crown; for example, the crown may have seven- or eight-fold symmetry, whereas the pavilion may have eight-fold or nine-fold symmetry, respectively.
  • the crown may not have perfect symmetry due to a difference in the number of first main crown facets compared to the number of second crown facets. In such cases, for convenience, the crown may be assumed to have a symmetry equal to the number of the first main crown facets.
  • the girdle is substantially circular - as best seen in Figures 3B and 3E .
  • Circular gemstones are commonly used for their optically pleasing symmetry.
  • other shapes are possible and envisaged within the scope of the invention, such as for example cushion shapes, oval shapes, etc.
  • Each of the sets of crown facets can be described by an angle (also referred to as an elevation angle or orientation), between the facets and the girdle plane P G .
  • ⁇ 1 is the angle between the facets 110 of the first set of main crown facets and the plane of the girdle P G
  • ⁇ 3 is the angle between the facets 130 of the third set of main crown facets and the plane of the girdle P G
  • ⁇ 2 is the angle between the facets 150 of the second set of crown facets and the plane of the girdle P G .
  • the angle ⁇ 2 between the facets of the second set of crown facets and the plane of the girdle P G is smaller than both (i) the angle ⁇ 1 between the facets 110 of the first set of main crown facets and the plane of the girdle P G , and (ii) the angle ⁇ 3 between the facets of the third set of (main) crown facets 130 and the plane of the girdle P G .
  • the angle ⁇ 2 between the facets of the second set of crown facets 150' and the plane of the girdle P G is smaller than the angle ⁇ 1 between the facets 110' of the first set of main crown facets and the plane of the girdle P G .
  • the use of a relatively shallow angle for the facets in the second set 150, 150', 150" of crown facets may advantageously reduce the risk of damage to the apex 200 of the crown (for example compared to a configuration that would simply extend the facets of the first main crown facets and optionally the third (main) crown facets to an apex), and may improve the ease of manipulation and application of the gemstone onto surfaces such as e.g. those of articles.
  • the angle ⁇ 1 between the facets 110 of the first type of main crown facets and the plane of the girdle P G may be larger than the angle ⁇ 3 between the facets 130 of the third set of (main) crown facets and the plane of the girdle P G .
  • the angle ⁇ 2 between the facets of the second set of crown facets 150 and the plane of the girdle P G may be at most about 26°, for example, between about 12° and about 26°, preferably between about 16° and about 21°.
  • angles ⁇ 2 between the facets of the second set of crown facets 150 and the plane of the girdle P G in the range of 19.2° ⁇ 0.75° are particularly advantageous in terms of brilliance in embodiments comprising a first and third set of (main) crown facets 110, 130.
  • angles ⁇ 2 between the facets of the second set of crown facets 150' and the plane of the girdle P G in the range of 18.2° ⁇ 2° are particularly advantageous in terms of brilliance in embodiments having a first set of main crown facets 110' and a second set of crown facets 150' (without having a third set of (main) crown facets).
  • angles ⁇ 1 between the facets of the first set of main crown facets 110' and the plane of the girdle P G may be at most about 43°, for example, between about 38° and about 43°.
  • angles ⁇ 1 between about 40.5° and about 43° may be particularly advantageous.
  • the inventors have in particular discovered that angles ⁇ 1 between the facets of the first set of main crown facets 110 and the plane of the girdle P G in the range of 42.2° ⁇ 0.75° are advantageous in terms of brilliance in embodiments comprising first and third sets of main crown facets 110, 130.
  • angles ⁇ 1 between the facets of the first set of crown facets 110' and the plane of the girdle P G in the range of 40.4° ⁇ 1.5° are particularly advantageous in terms of brilliance in embodiments comprising a first set of main crown facets 110' and a second set of crown facets 150' (without a third set of main crown facets).
  • the angle ⁇ 3 between the facets of the third set of main crown facets and the plane of the girdle may be at most about 38°, for example between about 33° and about 38°, preferably between about 35.5° and about 38°.
  • angles ⁇ 3 between the facets of the third set of (main) crown facets 130 and the plane of the girdle P G in the range of 36.1° ⁇ 0.75° are beneficial in terms of brilliance.
  • each of the facets 110, 130, 150; 110', 150' has a radial length l 110 , l 130 (where present), l 150 which is the longest length of the respective facet in the radial direction of the gemstone 100, 101 when viewed in plan from above.
  • the radial length l 110 , l 130 , l 150 is substantially identical for all of the facets in a set of facet types.
  • the radial length l 150 of the facets 150, 150' in the second set of crown facets is shorter than the radial length l 110 of the facets 110, 110' in the first set of main crown facets, and shorter than the radial length l 130 of the facets 130 in the third set of crown facets, if present.
  • the radial length l 150 of the facets 150, 150' in the second set of crown facets is at most 60%, at most 50%, at most 40% or at most 30% of the radial length l 110 of the facets 110, 110' in the first set of crown facets.
  • the radial length l 110 of the facets 110 is suitably between 80% and 120% of the radial length l 130 of the facets 130; for example, between 85% and 115%, between 90% and 100%, or between 95% and 105%.
  • the radial length l 110 of the facets 110 are approx. the same as the radial length l 130 of the facets 130, and the radial length l 150 of the facets 150 is at most 60%, at most 50%, at most 40%, or at most 30% of the radial length l 110 of the facets 110 and the radial length l 130 of the facets 130.
  • the radial length l 150 of the facets 150, in the second set of crown facets is at most 45%, at most 40%, at most 35%, at most 30% or at most 25% of the radius of the gemstone.
  • the radial length l 110 of the facets 110, in the first set of crown facets is at most 75%, at most 70%, at most 65%, at most 60%, or at most 55% of the radius of the gemstone.
  • the radial length l 130 of the facets 130, in the third set of crown facets is at most 80%, at most 75%, at most 70%, at most 65%, or at most 60% of the radius of the gemstone.
  • the radial length l 150 of the facets 150', in the second set of crown facets is at most 70%, at most 60% at most 50%, at most 40%, or at most 30% of the radius of the gemstone.
  • the radial length l 110 of the facets 110, in the first set of crown facets is at most 80%, at most 75%, at most 70%, at most 65%, or at most 60% of the radius of the gemstone.
  • Figure 4A shows the pattern of light reflections from shallow angle light
  • Figure 4B shows the pattern of light reflections from intermediate angle light
  • Figure 4C shows the pattern of reflections from steep angle light
  • Figure 4D shows the combined reflections from shallow, intermediate and steep angle light (see e.g. Figure 2A and 2B ).
  • This is in line with an aim of the invention to achieve light interaction properties, such as brilliance, to emulate that of an ideal brilliant cut gemstone, which may exhibit about 15% of steep-angle light areas, a high fraction of intermediate-angle light areas, and a small fraction of shallow-angle light areas.
  • the steep-angle light areas are evenly distributed and display a star-like pattern, and the steep-angle light areas do not comprise a large compact light area in the centre (at least compared to flat back gemstones of the prior art, as will be demonstrated further below).
  • the inventors have further found that the gemstone according to embodiments of the invention, such as that of Figures 3A to 3C , exhibits a high fire value (about 60%) and a high light return value (about 50% light return value relative to Spectralon®).
  • Figure 5A shows the pattern of light reflections from shallow angle light
  • Figure 5B shows the pattern of light reflections from intermediate angle light
  • Figure 5C shows the pattern of reflections from steep angle light
  • Figure 5D shows the combined reflections from shallow, intermediate and steep angle light.
  • the light interaction properties e.g. brilliance
  • the steep-angle light areas are evenly distributed and display a star-like pattern, and the steep-angle light areas do not comprise a large compact light area in the centre when compared to flat back gemstones of the prior art, as will be demonstrated further below.
  • the inventors have further found that the gemstone according to this embodiment has a high fire value (about 55%) and a high light return value (about 70.7% light return value relative to Spectralon®).
  • gemstones according to the invention have a relative light return of at least 30% and a fire of at least 40%.
  • the gemstone has a relative light return of at least 40% and a fire of at least 50%.
  • Light return and fire may be measured according to the Gemological Institute of America (GIA) standard as set out in Moses et al., 2004 (Gems & Gemology, Fall 2004, Vol. 40, No. 3, https://www.gia.edu/gems-gemology/fall-2004-grading-cut-quality-brilliant-diamond-moses ), as implemented in WO 2015/027252 A1 , which is incorporated herein by reference.
  • GAA Gemological Institute of America
  • Light return and fire properties for simulated gemstones may be simulated as explained below, for example, using a ray tracing software such as SPEOS from ANSYS (https://www.ansys.com/products/optical/ansys-speos).
  • Figures 6A, 6B and 6C show schematic side ( Figure 6A ), top ( Figure 6B ) and top side perspective ( Figure 6C ) views of a gemstone 100 according to embodiments of the invention, with a 6-fold symmetry of the crown facets.
  • the first set of main crown facets 110 has 6 substantially triangular facets with a curved broad side B 110 adjoining the girdle 140, alternating around the perimeter of the girdle with 6 kite-shaped main crown facets 130 of a third set of crown facets.
  • the crown 120 of the gemstone 100 further has 6 kite-shaped facets 150 in a second set of crown facets, which meet at an apex 200.
  • the gemstone 100 further comprises a flat back surface 160 parallel to the girdle plane P G .
  • the gemstone of this embodiment may have similar characteristics to those discussed above in relation to the gemstone of Figures 3A to 3C ; for example, similar angles ⁇ 1, ⁇ 2 and ⁇ 3 .
  • Figures 7A, 7B and 7C show schematic side ( Figure 7A ), top ( Figure 7B ) and top side perspective ( Figure 7C ) views of a gemstone 100 according to embodiments of the invention, with an eight-fold symmetry of the crown facets.
  • the first set of main crown facets 110 has 8 substantially triangular facets with a curved broad side B 110 adjoining the girdle 140, alternating around the perimeter of the girdle with 8 kite-shaped main crown facets 130 of a third set of crown facets.
  • the crown 120 of the gemstone 100 further has 8 kite-shaped facets 150 in a second set of crown facets, which meet at an apex 200.
  • the gemstone 100 further comprises a flat back surface 160 parallel to the girdle plane P G .
  • the gemstone of this embodiment may have similar characteristics to those discussed above in relation to the gemstone 100 of Figures 3A to 3C ; for example, similar angles ⁇ 1, ⁇ 2 and ⁇ 3 .
  • Figures 8A, 8B and 8C show schematic side ( Figure 8A ), top ( Figure 8B ) and top side perspective ( Figure 8C ) views of a gemstone 100 according to an embodiment of the invention, with a nine-fold symmetry of the crown facets.
  • the first set of main crown facets has 9 substantially triangular facets 110 with a curved broad side B 110 adjoining the girdle 140, alternating around the perimeter of the girdle with 9 kite-shaped main crown facets 130 of a third set of crown facets.
  • the crown 120 of the gemstone 100 further has 9 kite-shaped facets 150 in a second set, which meet at an apex 200.
  • the gemstone 100 further comprises a flat back surface 160 parallel to the girdle plane P G .
  • the gemstone of this embodiment may have similar characteristics to those discussed above in relation to gemstone 100 of Figures 3A to 3C ; for example, similar angles ⁇ 1, ⁇ 2 and ⁇ 3 .
  • Figures 9A and 9B show schematic side ( Figure 9A ) and top ( Figure 9B ) views of a gemstone 101 according to an embodiment of the invention, with an eight-fold symmetry of the crown facets.
  • the first set of main crown facets 110' has 8 substantially pentagonal facets with a curved broad side B 110 adjoining the girdle 140, adjoining each other with long sides L 110 .
  • the crown 120 of the gemstone 101 further has 8 kite-shaped facets 150' of a second set, which meet at an apex 200.
  • the gemstone 101 further comprises a flat back surface 160 parallel to the girdle plane P G .
  • the gemstone 101 of Figures 9A and 9B has radial lengths l 110 and l 150 which may have similar characteristics to those described above.
  • the gemstone 101 of Figures 9A and 9B with these parameters had a fire of about 52% and a light return relative to that of Spectralon® of 76.2%.
  • gemstone embodiments of the invention may have 6 first main crown facets and optionally 6 third (main) crown facets and 7 second crown facets; or may have 7 first main crown facets and optionally 7 third (main) crown facets and 8 second crown facets; or may have 8 first main crown facets and optionally 8 third (main) crown facets and 9 second crown facets; or may have 9 first main crown facets and optionally 9 third (main) crown facets and 10 second crown facets.
  • first main crown facets and optionally 6 third (main) crown facets and 8 second crown facets there may be 6 first main crown facets and optionally 6 third (main) crown facets and 8 second crown facets; or there may be 7 first main crown facets and optionally 7 third (main) crown facets and 9 second crown facets; or there may be 8 first main crown facets and optionally 8 third (main) crown facets and 10 second crown facets; or there may be 9 first main crown facets and optionally 9 third (main) crown facets and 11 second crown facets.
  • FIG. 19A and 19B Particular alternative embodiments of the gemstone of the invention are depicted schematically in Figures 19A and 19B and in Figures 20A and 20B .
  • the gemstone 102 of Figures 19A and 19B has 7 first main crown facets 110" and 8 second crown facets 150"; whereas the gemstone 102 of Figures 20A and 20B has 8 first main crown facets 110" and 9 second crown facets 150".
  • the gemstones of Figures 19 and 20 could equally be modified to include 7 or 8 third (main) crown facets respectively.
  • the facets of the second type may have different geometries to one another.
  • the crown facets of the second type may include both triangular and kite-shaped facets, wherein the kite-shaped facets may be irregular (i.e. not formed of two major sides of identical length and two minor sides of identical length).
  • the triangular facets may not be equilateral or isosceles triangles, but rather may be scalene triangles.
  • the refractive index of the material of the gemstone is at least about 1.45.
  • the material of the gemstone has a refractive index of at least about 1.5 and not more than about 1.8, such as between about 1.55 and about 1.7.
  • Physical properties like the refractive index influence the path of the light through a gemstone. As such, refractive indices within these ranges may further increase the brilliance of the gemstone.
  • a particular refractive index for the gemstones of the invention is 1.56.
  • the gemstone is made of a transparent material.
  • transparent' is used throughout this disclosure to refer to a material that has a transparency higher than zero.
  • a material is called transparent if it allows the transmittance of light, suitably at least visible light.
  • the material is transparent in the conventional sense, i.e. allowing (at least visible) light to pass through the material without being scattered.
  • the gemstone can be made of a wide variety of materials.
  • the gemstone is made of glass, plastic or cubic zirconium.
  • the gemstone is made of crystal glass.
  • Transparent bodies made of glass or plastic are preferred, because they are low cost, non-conductive and are most readily provided with facets.
  • Gemstones made of glass, and in particular crystal glass e.g. as defined by the European Crystal Directive (69/493/EEC)), can be particularly beneficial, for their superior optical properties.
  • the invention is not limited in principle with respect to the composition of the glass.
  • 'Glass' in this context means any frozen supercooled liquid that forms an amorphous solid.
  • Oxidic glasses, chalcogenide glasses, metallic glasses or non-metallic glasses can be employed.
  • Oxynitride glasses may also be suitable.
  • the glasses may be one-component (e.g. quartz glass) or two-component (e.g. alkali borate glass) or multicomponent (e.g. soda lime glass) glasses.
  • the glass can be prepared by melting, by sol-gel processes, or by shock waves. Such methods are known to the skilled person.
  • Inorganic glasses, especially oxidic glasses are preferred. These include silicate glasses, soda lime glasses, borate glasses or phosphate glasses. Lead-free crystal glasses are particularly preferred.
  • the gemstone is made of soda lime glass.
  • the faceted transparent body may alternatively be made of lead and barium-free crystal glass. Examples of suitable lead and barium-free crystal glass compositions for use in the present invention are disclosed in EP 1725502 and EP 2625149 , the contents of which are incorporated herein by reference.
  • plastics can be employed as another raw material for the preparation of the gemstone.
  • Transparent plastics are preferred.
  • acrylic glass polymethyl methacrylates, PMMA
  • PC polycarbonate
  • PVC polyvinyl chloride
  • PS polystyrene
  • PPO polyphenylene ether
  • PE polyethylene
  • PMMI poly-N-methylmethacrylimide
  • An advantage of using a plastics material over glass in the manufacture of transparent bodies for use in the present invention resides, in particular, in the lower specific weight, which is only about half that of glass.
  • other material properties may also be selectively adjusted.
  • plastics are often more readily processed as compared to glass.
  • a preferred plastic is poly-N-methylmethacrylimide, which is sold, for example, by Evonik under the name Pleximid® TT70.
  • Pleximid® TT70 has a refractive index of 1.54, and a transmittance of 91 % as measured according to ISO 13468-2 using D65 standard light.
  • the gemstone is coloured.
  • the colouring is provided as a colouring agent throughout the material of the gemstone.
  • a colouring may be provided as a coating or surface treatment on at least a region of a surface of the gemstone.
  • a coating or surface treatment may be provided on at least a region of the crown facets and/or at least a region of a substantially flat back surface of the gemstone.
  • Colouring and decorative coatings may enable the gemstone to be provided with a variety of decorative effects, improving their flexibility of use. Colourings and decorative coatings are preferably configured such that the gemstone remains transparent to light entering through the crown facets.
  • the largest transverse dimension of the gemstone (also referred to herein as its diameter) may be between 1 and 80 mm, between 1 and 60 mm, between 1 and 40 mm, between 1 and 20 mm, or between 2 and 12 mm.
  • the girdle may be substantially circular. In embodiments where the girdle is not substantially circular, the term 'diameter' may refer to the diameter of the smallest circle that would fit the geometry of the girdle.
  • a reflective layer is provided on substantially the whole of the back surface 160 of the gemstone.
  • the reflective layer is a metallisation layer.
  • the reflective layer comprises one or more metals selected from silver, aluminium and rhodium. Reflective layers such as metal coatings are known in the art.
  • the reflective layer is provided on a region of the back surface of the gemstone that covers most (such as e.g. 90%, 95%, 98%, or 99%) of the surface of the back surface of the gemstone.
  • one or more layers of adhesive and/or one or more protective layers may be provided on substantially the whole of the back surface of the gemstone.
  • the use of pre-applied adhesive may enable easy application of the finished decorative element to the surface of an article.
  • a protective layer may advantageously protect the gemstone or a reflective layer applied thereon from damage, particularly before the gemstone is attached to a surface.
  • a layer of non-reactive thermal adhesive may be provided on the back surface of the gemstone.
  • a pre-applied hot-melt adhesive may enable easy application of the gemstone to many surfaces including e.g. garments and textiles, etc.
  • the layer of hot melt adhesive has a thickness between 100 ⁇ m and 200 ⁇ m.
  • layers of hot melt adhesive in the above range may provide for sufficient adhesion even on porous substrates such as textiles.
  • the layer of hot melt adhesive is too thick, the risk of the hot melt adhesive spilling out when the decorative element is applied to a surface increases, resulting in possible application problems, loss of aesthetic quality, and waste of adhesive.
  • the hot melt glue may be a copolyamide-based glue, such as Griltex® 1A from EMS-CHEMIE.
  • the hot melt glue may be a thermoplastic polyurethane-based glue, such as VP 1006 by Collano® AG.
  • the protective layer comprises a layer of lacquer.
  • the lacquer may be applied with a thickness of between about 4 and 14 ⁇ m (i.e. 9 ⁇ 5 ⁇ m); for example, the lacquer may be applied with a thickness of about 9 ⁇ m.
  • the layer of lacquer comprises a lacquer selected from the group consisting of: epoxy lacquers, one component polyurethane lacquers, bi-component polyurethane lacquers, acrylic lacquers, UV-curable lacquers, and sol-gel coatings. The lacquer may additionally ensure that the gemstone according to the invention is bondable.
  • a suitable lacquer may depend on the material to which the gemstone is intended to be bonded, and/or on the adhesive that is intended to be used.
  • the lacquer may optionally be pigmented.
  • the lacquer is applied by spraying, digital printing, rolling, curtain coating or other two-dimensional application methods known in the art.
  • the gemstones according to the invention are particularly suitable as decorative elements for use on garments, wearables, fashion accessories, etc. where the combination of a flat back surface as well as the aesthetic potential afforded by the use of a gemstone with improved optical properties are important.
  • the invention also encompasses an article comprising one or more gemstones according to the first and/or second aspect of the invention.
  • the article may be a clothing accessory such as shoes, a hat, sunglasses, glasses, bags, jewellery such as a bracelet, necklace or watch, an electronic wearable such as an activity tracker, etc., a piece of clothing such as a shirt, jacket, jumper etc., a consumer electronics item such as laptop, phone, tablet, etc.; a packaging article such as a box, can, jar, etc., a homeware article such as a frame, mirror, crockery item, etc.
  • Articles also include vehicles, such as cars, boats etc.
  • gemstone with flat backs were studied for their optical properties.
  • Figure 10A illustrates a schematic front side perspective view of a flat back gemstone 1001 according to the prior art, with a simple cut (referred to as 'A2000 cut') having a single set of crown facets 1100' extending between a table 1200 and a girdle 1400.
  • Figure 10B shows a schematic front side perspective view of a flat back gemstone 1000 according to the prior art, with an advanced cut (referred to as 'A2078 cut') comprising a first and a third (according to the nomenclature used for embodiments of the invention described above) set of crown facets 1100, 1300 extending between a girdle 1400 and a flat table 1200.
  • the table 1200 of gemstone 1000 had a shortest diameter of 1.55 mm and the table 1200 of gemstone 1001 has a shortest diameter of 1.15 mm.
  • the gemstone of Figure 10A had a diameter of 3.1 mm, a girdle height of 0.31 mm and facets 1100' have an angle of 42.0° relative to the plane of the girdle.
  • the gemstone of Figure 10B had a diameter of 3.1 mm, a girdle height of 0.18 mm, facets 1300 have an angle of 34.2° relative to the plane of the girdle, and facets 1100 have an angle of 40.7° relative to the plane of the girdle. In both cases the table facet 1200 has an angle of 0° to the girdle plane.
  • a directed white light source illuminating the gemstone from the top through an aperture of 2x0.25°, i.e. 0.5° was used.
  • the coloured reflections on an observing surface (a 1 m x 1 m flat observing surface placed parallel to the girdle plane and at 0.5 m above the girdle plane), from the light incident on the gemstone were then analysed.
  • the pattern of light reflections associated with the gemstone of Figures 10A and 10B were also simulated for shallow, intermediate and steep-angle light, as explained above in relation to Figures 2A and 2B .
  • Figures 11A, 11B, 11C and 11D show the pattern of light reflections associated with the gemstone of Figure 10A .
  • Figure 11A shows the pattern of light reflections from shallow angle light
  • Figure 11B shows the pattern of light reflections from intermediate angle light
  • Figure 11C shows the pattern of light reflections from steep angle light
  • Figure 11D shows the combined light reflections from shallow, intermediate and steep angle light.
  • the gemstone 1001 has about 32% of steep angle light reflection areas (compared to an ideal of about 15%), with 64% intermediate and 4% of shallow light reflections.
  • the gemstone 1001 comprised a large compact steep-angle light area in the centre of the gemstone (see Figure 11C ), and the steep-angle light areas were not distributed in a star-like pattern.
  • Figures 12A, 12B, 12C and 12D show the pattern of light reflections associated with the gemstone of Figure 10B .
  • Figure 12A shows the pattern of light reflections from shallow angle light
  • Figure 12B shows the pattern of light reflections from intermediate angle light
  • Figure 12C shows the pattern of light reflections from steep angle light
  • Figure 12D shows the combined light reflections from shallow, intermediate and steep angle light.
  • the gemstone 1000 comprised a smaller compact steep-angle light area in the centre of the gemstone (see Figure 12C ) compared to gemstone 1001 of Figure 10A , but this was still relatively large (about 1.15-1.2 mm). Additionally, the steep-angle light areas were not distributed in a star-like pattern (see Figure 12C ).
  • Figure 12E shows the simulated illuminance of the prior art gemstone of Figure 10B along a section through the bright area of the gemstone at the point and orientation indicated by a short white line in Figure 12D , demonstrating a large central area of light transmission / reflection through the centre of the gemstone.
  • the inventors sought to improve on the flat back gemstones of the prior art (Example 1), by providing new geometries: (i) according to an exemplary embodiment of the invention as shown in Figures 3A to 3C (referred to as 'invented cut' herein and in Figure 13 ); (ii) a geometry that represents a simple adaptation of the geometry of the prior art gemstone illustrated in Figure 10A , wherein the crown facets 1100' are extended towards the middle of the gemstone to form an apex (referred to as 'A2000m' herein and in Figure 13 ); and (iii) a geometry according to the invention similar to that shown in Figures 3D and 3E , wherein the second set of crown facets are transformed to elongated kite-shaped facets that extend over half way from the apex of the gemstone towards the girdle of the gemstone (referred to as 'A2078m' herein and in Figure 13 ).
  • Figure 21 shows the quantified fire value (relative to the maximum fire possible) and light return value (relative to the light return of Spectralon®) for embodiments according to the first aspect of the invention as illustrated in Figures 9A and 9B (marked as 'invented cut 2') and Figures 3A to 3C (marked as 'invented cut') in comparison to the embodiment termed 'A2078m' and the comparative gemstone cut termed A2000m both of which are described above.
  • Figures 14A, 14B, 14C and 14D show the pattern of light reflections associated with the gemstone of the invention termed 'A2078m' above and in Figure 13 .
  • Figure 14A shows the pattern of light reflections from shallow angle light
  • Figure 14B shows the pattern of light reflections from intermediate angle light
  • Figure 14C shows the pattern of light reflections from steep angle light
  • Figure 14D shows the combined light reflections from shallow, intermediate and steep angle light.
  • the gemstone A2078m has about 7% of steep angle light reflection areas (compared to an ideal of about 15%).
  • the gemstone A2078m has 84% of intermediate angle light reflection areas and about 9% of steep angle light reflection areas (which is broadly in line with the ideal high proportion of intermediate angle light reflection areas and small proportion of shallow angle light reflection areas exhibited by a brilliant cut gemstone); and is better than the corresponding gemstone of the prior art as shown in Figure 10B .
  • the gemstone A2078m still comprises an area of steep-angle light reflection in the centre of the gemstone (see Figure 14C ), but this is far more compact than in the corresponding prior art gemstone of Figure 10B .
  • Figure 15A, 15B and 15C show an investigation of the luminance due to reflection of steep angle light through the bright area in the centre of the gemstone marked as 'A2078m" on Figure 13 .
  • Figure 15A shows the pattern of reflections from steep angle light associated with this gemstone (identical to Figure 14C ) along the short line (angled from upper left to lower right) and the long line (approx. horizontal) through the central bright area indicated by white lines in Figure 15A.
  • Figure 15B shows the simulated illuminance along the long, horizontal line in Figure 15A
  • Figure 15C shows the simulated illuminance along the short, inclined line shown in Figure 15A
  • the data in Figures 15B and 15C show that the gemstone A2078m has a bright central area of about 1.1 mm along the long axis and about 0.6 mm along the short axis.
  • Figures 16A and 16B show an investigation of the luminance due to reflection of steep angle light through the bright area in the centre of a gemstone according to the invention with three sets of crown facets, marked as "invented cut” on Figures 13 and 21 and illustrated in Figures 3A to 3C .
  • Figure 16A shows the pattern of reflections from steep angle light associated with this gemstone (identical to Figure 4C ), with the section through the central bright area indicated by a white line.
  • Figure 16B shows the simulated illuminance along the section indicated by the white line shown in Figure 16A .
  • This data indicates that the gemstone according to embodiments of the invention with three sets of crown facets has a central bright area of 0.64 mm, which is about 50% less than for A2078. Therefore, this data shows that the gemstone of the invention provides improved fire properties as well as the pattern of light reflections from at least steep angle areas compared to flat back gemstones according to the prior art.
  • Figure 17 shows the quantified fire value (relative to the maximum fire possible) and light return value (relative to the light return of Spectralon®) for various embodiments of the invention.
  • the point labelled 'invented cut' shows the results for a gemstone of the invention as shown on Figures 3A to 3C having seven-fold symmetry
  • the point labelled 'invented cut, sym8' shows the results for a gemstone of the invention as shown in Figures 7A to 7C having eight-fold symmetry
  • the point labelled 'invented cut, sym6' shows the results for a gemstone of the invention as shown in Figures 6A to 6C having six-fold symmetry
  • the point labelled 'invention cut, sym9' shows the results for a gemstone of the invention as shown in Figures 8A to 8C having nine-fold symmetry.
  • This data shows that similarly high fire and light return values can be obtained with six-, eight- and nine-fold symmetries according to embodiments of the invention.
  • the inventors sought to show that the beneficial results demonstrated above with gemstones of the invention having three sets of crown facets can be replicated with gemstones according to embodiments of the invention having just a first and a second set of crown facets.
  • the following gemstones were simulated and their fire value (relative to the maximum fire possible) and light return value (relative to the light return of Spectralon®) were quantified:
  • the inventors sought to demonstrate that the beneficial results evidenced above for gemstones of the invention having six, seven, eight or nine-fold symmetry can be mirrored with gemstones according to embodiments of the invention having non-perfect symmetry.

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2270270A (en) * 1940-04-20 1942-01-20 Clare Philip Molded plastic gem
US3796065A (en) * 1970-12-01 1974-03-12 Joostes Diamond Cutting Works Stone with emerald cut crown and modified brilliant cut base
EP1725502A1 (de) 2004-03-19 2006-11-29 D. Swarovski & Co. Blei- und bariumfreies kristallglas
EP2625149A1 (de) 2011-09-01 2013-08-14 Preciosa, A.S. Kristallglas mit brechungsindex über 1,53 ohne blei-, barium- und arsenverbindungen
WO2015027252A1 (de) 2013-08-27 2015-03-05 D. Swarowski Kg Anordnung zur analyse eines durch brechung und reflexion an einem schmuckstein hervorgerufenen lichtmusters

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2270270A (en) * 1940-04-20 1942-01-20 Clare Philip Molded plastic gem
US3796065A (en) * 1970-12-01 1974-03-12 Joostes Diamond Cutting Works Stone with emerald cut crown and modified brilliant cut base
EP1725502A1 (de) 2004-03-19 2006-11-29 D. Swarovski & Co. Blei- und bariumfreies kristallglas
EP2625149A1 (de) 2011-09-01 2013-08-14 Preciosa, A.S. Kristallglas mit brechungsindex über 1,53 ohne blei-, barium- und arsenverbindungen
WO2015027252A1 (de) 2013-08-27 2015-03-05 D. Swarowski Kg Anordnung zur analyse eines durch brechung und reflexion an einem schmuckstein hervorgerufenen lichtmusters

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
J. SASIAN ET AL.: "Optical Engineering", vol. 46, 2007, AMERICAN GEMOLOGICAL SOCIETY, article "Evaluation of brilliance, fire, and scintillation in round brilliant gemstones", pages: 093604
MOSES ET AL., GEMS & GEMOLOGY, vol. 40, no. 3, 2004, Retrieved from the Internet <URL:https://www.qia.edu/qems-qemoloqy/fall-2004-qradinq-cut-quality-brilliant-diamond-moses>
P. YANTZER ET AL., FOUNDATION, RESEARCH RESULTS AND APPLICATION OF THE NEW AGS CUT GRADING SYSTEM, Retrieved from the Internet <URL:https://cdn.vmaws.eom/www.americanqemsociety.orq/resource/resmqr/docs/AGSLab/AGS-Cut-System.pdf>

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