EP0016885A1

EP0016885A1 - Cut gemstone, method and apparatus for producing it

Info

Publication number: EP0016885A1
Application number: EP79302801A
Authority: EP
Inventors: Roger Maxwell Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-12-06
Filing date: 1979-12-05
Publication date: 1980-10-15
Also published as: JPS55101361A; IL58834A0; IL58834A

Abstract

Gemstones are cut such that the pavillion facets are curved facets (12,14,16) and are arranged in pairs around the pavillion and so disposed relative to each other and the crown and table of the gemstone that light entering the stone through the crown and meeting the first curved facet of a pair is converged and reflected on to a second curved facet of that pair from which it is reflected to the crown; faceting machine for producing such facets is disclosed.

Description

This invention concerns gemstones, a method of cutting and/or polishing the same to improve their brilliance and a facet-ing machine for enabling the method to be carried out.
Gem cutters use standard cuts to achieve brilliance depending upon the shape of the uncut gemstone. Hitherto the facets of gemstones have been flat and the standard cuts cause incident light to be brought to a focus either within the stone or a short distance above the crown of the stone and consequently the full possibilities o.f brilliance are not realised.
Terms used for parts of the gemstone are standard and are, the crown (the portion of the stone above the girdle), the girdle (the peripheral line of greatest dimension), the table (the flat upper portion of the stone normally viewed through which light enters and leaves the stone), the pavillion (the bulky portion of the stone below the girdle in which is liberally faceted to achieve light reflection), and the culet (the lower most portion of the pavillion).
This invention provides a gemstone having a crown portion which tapers from a girdle and a pavillion portion tapering from the opposite direction to the crown and terminating in a culet and facets on the pavillion characterised in that each facet of the pavillion is a curved facet which term includes a single surface which is part of a cone or one which is curved in a first direction and flat in the direction substantially at 90° to the first direction ofr is a of smaller flat surfaces the lateral extremities of which lie on the arc of a circle or the surface of the sphere or ellipsoid, and in that the curved facets are arranged in pairs and are so disposed relative to each other and the crown and table that light entering the stone through the crown and meeting the first curved facet of a pair is converged and reflected onto the second curved facet of that pair from which it is reflected to the crown of the gemstone.
The pavillion may have a ring of circumferential curved fatets adjacent the table, a ring of circumferential curved facets at the culet and one or more further rings of circumferential curved facets between the table ring and the culet ring, each ring defining a plane which is parallel to the table, all the facets of the same ring subtending the same angle with reference to the plane of the table and each successive ring in the direction from the table to the culet subtending a successively diminishing acute angle with the plane table whereby light which enters the crown, perpendicularly to the table undergoes a reflection at both curved facets of a pair and is reflected toward the eye of an observer in a direction at substantially perpendicular to the crown. Each curved facet of each pair of curved facets is arranged equally about an axis of symmetry of the gemstone. Alternatively, the pairs of curved facets are disposed in common plane at an angle to one another, that is to say, the pairs need not be diametrically opposite one another in the gemstone and in an asymmetrically shaped stone one curved facet may direct light onto the next adjacent facet rather than the facet which is directly opposite. The radius of the curved facets in the pavillion is greater than half the maximum distance across the girdle. Preferably the radium is of the order of the maximum distance across the girdle. The radius is preferably such as to cause light rays converged by ineidenes upon the first curved facet of the pair to sonverge buy not to diverge within the stone before reaenitng the seccaa eurved facet of the pair.
The invention also provides a method of cutting gemstones as defined above by shaping a series of pairs of curved facets so that the light rays entering at or close to 90⁰ to the table and falling on the first of the pair of faceted arcs are concentrated and reflected to the second of the pair of facets which in turn deflects the converged rays falling upon it from the first facet, into substantially parallel rays which are reflected back to the crown where allowing where applicable for refraction, much of the light emerges within the range of vision of an observer as a series mf bright light beams in which the rays are substantially parallel.
The invention also provides a faceting machine for cutting gemstones comprising a movable lapping surface, a quill positioned close to the lapping surface, a holder projecting from said quill having means for supporting a radius arm at a plurality of preselected positions and a dopstick support pivotally connected at or near one end of said radius arm.
The end of the radius arm nearest the pivotal connection carries a scale and the dopstick support has an indicator which moves over said scale thereby indicating the angular disposition of the gemstone axis to the radius arm. The radius arm may be cranked.
Examples of the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 is a plan of a symmetrical gemstone showing pairs of curved facets.
Figure 2.is a plan of an asymmetric stone showing the arrangement of the pairs of curved facets.
Figure 3 is a diagrammatic elevation of a gemstone showing the paths of various light rays through the gemstone.
Figure 4 is a diagrammatic elevation'of the same gemstone showing the path,,of an oblique ray through the gemstone.
Figure 5 is a plan of the pair of facets shown in Figure 4 to demonstrate the path of the oblique ray shown in Figure 4.
Figure 6 is a diagrammatic elevation of the same gemstone showing the path of an oblique ray througs the gemstone.
Figure 7 is a plan of the pair of facets shown in Figure 6 to demonstrate the path of the oblique ray in Figure 6.
Figure 8 is a diagrammatic side elevation of the faceting apparatus; and
Figure 9 is a diagrammatic side elevation of a gemstone with various measurements marked thereon to show the way in which the curved facets are laid out and applied by the faceting machine.

Referring firstly to Figures 1 and 3, the stone is symmetrical in layout, being substantially pyramidal having a pavillion 2 defined by four main faces 4. The crown 6 of the stone is flat and the culet 8 is centrally beneath the table 10. Each quandrant of the stone has a curved facet 12 adjacent the girdle, a curved facet 14 adjacent the culet 8 and an intermediate curved facet 16. As each quandrant is alike the curved facets are arranged in pairs and form rings as can be best seen in Figure 1. The curved facets 12, are of a radius about equal to the diagonal of the gemstone girdle. Each curved facet 12, 14, 16 is the product of several flat facets, one of which is indicated as 18. The curved facets 12. 14, 16 are each disposed at a slightly different acute angle with respect to the table being at say 42° 42° and 44° and in consequence the light which enters the crown b in more or less perpendicular direction thereto is reflected parallel to the plane of the table from one curved facet 12 to the mutually opposite curved facet 122 which is the paired facet.
Figure 2 shows an asymmetrical stone wherein the pairs of curved facets are not geometrically opposite each other. The light reflected from curved facet le will impinge- on two curved facets 162 and 164, but 164 may alsc b₂ paired with 166 for some light rays. The cuvatore of the curved facets 12, 14, 16 ensures that the inteinal reilecien ef the light also produces a convergence and therefore an inerease in light intensity which emerges from the stone after a second reflection.
Not all light rays are nearly perpendicular to the crown of the stone and when an oblique ray enters the crown as shown in Figure 4, the first incidence of the ray on facet 16 which is in effect the segment of a cone, directs the light downwardly into the stone and no longer is the ray a part of the plane of a circle. The angular dip causes the ray to travel from a curved surface as shown in Figure 5 with a radius of a circle to a smaller curved surface which defines the edge of an elliptical plane. Though the curved facet 14 is still a segment of a cone, the elliptical plane into which these rays are diverted after the first incidence is not efficient for reflection toward the crown of the stone. This is compensated to some extent by selecting a radius for the curved facets which will cause the rays to converge, but not to focus and then diverge within the stone between the pair of curved facets.
The reverse situation is shown in Figure 6 and 7. Here a perpendicular central ray undergoes its first reflection at a curved facet 14 of the culet 8 and a second reflection at the curved, paired facet 12. Convergence results but not an increase in intensity of light as once again the rays are confined within an elliptical plane.
Thus it will be seen that the length of the radius is critical and for a correct understanding, reference is made both to Figure 9 and to the parts of the faceting machine shown in Figure 8. Referring to the latter, the quill 18 which has a protractor (not shown) supports a cranked holder 20. A radius arm 22 graduated in hundredths of an inch is held in the bore of the holder by a finger screw 24. A protractor scale 26 is fixed to the radius arm and the arm also supports a dopstick holder 28 for a gemstone 30 to which holder is attached a pointer 32. A clamping screw 34 secures the holder 28 and pointer in any one of a number of selected positions in relation to the lapping surface 36 (two positions of which are shown).
Referring now to Figure 9 the radius may be calculated from a plan of the stone or the stone may be preformed and the length of travel of the light ray which each curved facet is to concentrate, may be accurately measured. This length bears no relation to the diameter or thickness of the gemstone at the point of the centre of the facet. In Figure 9 there is shown an arc of facets to be cut at B, of which each facet is at angle F to the table 10. The radius is calculated from the length BC. This length is reduced or increased usually by 10 to 20% depending on the curvature of the arc at point C, so as to turn the rays parallel to each other. The angle Q which the ray makes with the facet to be cut at B is set on the main quill protractor. The angle F is the facet angle. The angle I is the difference between angle F and angle Q. Angle I is set on the protractor 26 which ensures that the stone is turned in such a direction in relation to the lapping surface that the arc is cut so that it is circular in the planar reflection BC but is elliptical in the plane of the table FE.
From the corrected length BC the dimension to be set on the radius arm is calculated by the equation:-

Where C equals dimension required, R is corrected length BC, L is the distance from the fulcrum made by the clamping screw 24 to the centre of the arc of facets to be cut, and T is the distance between the centre of the arc and the vertical line through the centre of the stone (usually half the diameter of the stone at the arc to be cut).
I have found the advantages of the above cuts to be as follows.
The waste of gemstone material is reduced. Stones of irregular shape may be cut to show the same degree of brilliance as a stone of regular shape. A greater vaydety of shapes is possible that is the stone need net be neund to conform with the "step" "trap" or "emerald" eut. My lethod acnieves the same degree of brilliance in any shape of stone except a long thin stone. Darker stones which were formerly too dark or too milky to provide any brilliance are now commercial possibilities. The concentration of brilliance hides the pavillion facets and gives the impression that there is a light source within the stone. The shape of the brilliance as distinct from the shape of the stone may be controlled. The brilliance may be made to appear as a bar, a cross, a flower or a cluster of stars.

Claims

1. A gemstone having a crown portion which tapers from a girdle and a pavillion portion tapering from the opposite direction to the crown and terminating in a culet, facets on the pavillion characterised in that each facet of the pavillion is a curved facet which term includes a single surface which is part of a cone or one which is curved in a first direction and flat in the direction at substantially 90° to the first direction or is a series of smaller flat surfaces the lateral extremities of which lie on the arc of a circle or the surface of a sphere or ellipsoid and in that the curved facets are arranged in pairs and are so disposed relative to each other and the gemstone crown and table that light entering the gemstone through the crown and meeting the first curved facet of a pair is converged and reflected onto the second curved facet of that pair from which it is reflected to the crown of the gemstone.

2. A gemstone as claimed in Claim 1 having a pavillion defined by a ring of circumferential curved facets adjacent the table, a ring of circumferential curved facets at the culet and one or more further rings of cireumferential curved facets between the table ring and the culet ring each ring defining a plane which is parallel to the table, all the facets of the same ring subtending the same angle with reference to the plane of the table and each successive ring in the direct. in from the table to the culet subtending a-successive diminishing acute angle with the plane of the table whereby light which enters the crown, perpendicularly to the table undergoes a reflection at both curved facets of a pair and is reflected towards the eye of an observer in a direction substantially perpendicular to the crown.

3. A gemstone as claimed in Claim 1 or 2, wherein each curved facet of each pair of curved facets is arranged equally about an axis of symmetry of the gemstone.

4. A genstone as claimed in Claim 1 or 2, wherein the pairs of urved facets are disposed in a common plane at an angle to - one another.

5. A gemstone as claimed in any one of Claims 1 to 4, wherein the radius of the curved facets in the pavillion is of the order of the distance of travel of a light ray from a first incidence upon one facet to a second incidence upon a paired facet in a plane parallel to the table.

6. A gemstone as claimed in Claim 5, wherein the radius is of the order of the maximum distance across the girdle.

7. A gemstone as claimed in Claim 5 or 6, wherein the radius is such as to cause light rays converged by incidence upon the first curved facet of a pair to converge but not to focus and diverge within the stone before reaching the second curved facet of the pair.

8. A gemstone as claimed in any one of Claims 1 to 7, wherein the crown is also provided with pairs of eurved facets in like manner to the pavillion.

9. A method of cutting gemstones as claimed in Claim 1 by shaping a series of pairs of curved facets so that the light rays entering at or close to 90° to the table and falling or the first of a pair of faceted arcs are concentrated and reflected to the second of the pair of facets which in turn deflects the converged rays falling upon it from the first facet into parallel rays which are reflected back to the crown, where allowing where. applicable for refraction, much of the light emerges within the range of vision of an observer as a series of substantially parallel bright light beams in which the rays are substantially parallel.

10. A faceating machine for catting gemstones as claimed in Claim 1 eompristin a mevable lapping surface, a quill position clese to the lapping surface, a soldes projecting fiem said quill having means for supporting a radius arm and a plurality of preselected positions and a capacity support pivotably connected at or near one end of said radius arm.