IE42227B1 - Impovements in or relating to methods of polishing diamonds - Google Patents

Abstract

A method is provide for polishing a gemstone and to a novel gemstone per se. The method includes the steps of forming a table, polishing an off number of faces on a base, which faces converge to a point and forming a plurality of facets on the girdle of the stone between the base and the table whereby the inclination of the faces with respect to the table is such that light entering the table substantially normal thereto is internally reflected to the opposite corner where it is subsequently internally reflected back to the face of initial incidence and out of the upper part of the stone to impart brilliance thereto. The gemstone is characterised by having a tuble portion defined by a table and a girdle having a periphery greater than the periphery of the table to define a pyramidal table portion and a base defined by a plurality of faces converging towards a point on the side of the gridle opposite the table portion which stone has an odd number of sides, the inclination of the faces to the plane of the table permitting light entering the table substantially normal thereto to be internally reflected at an opposite corner for subsequent internal reflection at the face of initial incidence and out of the upper part of the stone to impart brilliance thereto. Gemstones in accordance with aspects of the present invention particularly include maccle diamonds which are capable of being cut in accordance with the method of an aspect of this invention to produce gemstones having improved brilliance with a reduced amount of waste from the uncut stone.

Description

TATENT APPLICATION BY (71) TOYE GEMSTONES LIMITED, A BRITISH COMPANY OF REGALIA HOUSE, 19-21, GREAT QUEEN STREET LONDON WC2 5BE, ENGLAND.

Price I2ip The present invention relates to the polishing of gemstones · and has particular reference to polishing of diamonds.

It has been well known that to polish gemstones to provide a degree of brilliance therein, the stones are polished to form a substantially flat table at the top, the lower part of the stone being provided with a plurality of faces which converge towards a point.

The arrangement is such that in order to impart a brilliance or sparkle to the stone, the angle between the faces and the table needs to be such that light entering the table is internally reflected by two or more faces before leaving the stone via the table, thus imparting the brilliance to the cut stone.

It is quite clear, therefore, that depending upon the gemstone the angle between the faces defining the lower part of the stone and the table is critical since if the reTections are such that the light is internally reflected at one or more faces and leaves the stone other than through the table, the stone will have a dead or lifeless appearance.

This technique of polishing is extremely well known in the diamond art where the polishing of stones for brilliance is most usually practised..

Many diamonds, however, are of dimensions and have cleavage planes therein, such that it is difficult to obtain the desired shape and critical angle between the base faces and the table without the wastage of substantial quantities of the stone. In particular made diamonds are virtually incapable of being polished by the method - 2 42287 described above without substantial wastage. Made diamonds in general have a pyramidal form with a generally three-sided periphery or girdle. In the unpolished form the sides of the girdle are generally convex and in polishing are left substantially in that form.

The stones are generally flat and in order to produce a stone which has any substantial brilliance by the method described above, ittjis necessary to remove considerable quantities of the stone in order to obtain the desired angle.

According to the present invention, there is provided a method of polishing a gemstone, which method comprises forming a table, a girdle having a periphery greater than the periphery of the table to , define an intermediate portion therebetween,and a base extending from the opposite side of the girdle from the intermediate portion, polishing an odd number of converging faces on the base and forming a plurality of facets on the girdle of the stone, the inclination of the faces with respect to the table being such that light entering the table substantially normal thereto is internally reflected at a said face to a corner opposite thereto where it is internally reflected back to the said face and thence out of the table to impart brilliance to the stone.

The invention also includes a gemstone having a table, a girdle having a periphery greater than the periphery of the table to define an intermediate portion therebetween, and a base on the opposite side of the girdle from the table portion, which base has an odd number of converging faces, the inclination of the planes of the faces to the plane of the table permitting light entering the table substantially normal thereto to be internally reflected at one said face to a corner - 3 42327 opposite thereto where it is internally reflected back to the said face and thence out of the table to impart brilliance to the stone.

The gemstone may be a diamond and the diamond may be a made diamond. The gemstone may be a relatively flat stone and may be polished with three faces on said base. Each face may be convexly faceted to assist reflection of the face towards the opposite corner. The facets on the girdle are preferably perpendicular to the table and in the case of a diamond the angle between the planes of the faces and the table may be within the range of 25° to 40°.

Thus, in accordance with the present invention the depth of the stone on polishing is substantially reduced over that which is necessary to obtain brilliance in the stone by reflection in opposite faces or facets on the base. The faces may extend to a point or may be truncated as may be desirable.

Two facets may be polished on each convex face and a corner facet may be polished on each corner of the girdle between adjacent convex faces.

The facets polished on the girdle permit facets to be polished on the portion between the table and the girdle and on the base faces of the made.

Following is a description by way of example only and with reference to the accompanying drawing of one method of carrying the invention into effect:Figure 1 is a top plan view of a made diamond polished in accordance with the present invention; Figure 2 is an under plan view of the diamond of Figure 1, and Figure 3 is a side view of the diamond of Figure 1; -443327 Figure 4 is a further simplified side view of the stone shown in Figures 1-3; Figure 5 is a simplified plan view of the stone shown in Figures 1-3, and Figure 6 is a perspective view showing a light path within the stone of the present invention.

Figures 1 to 3 show a made type diamond 10 having a table 11, a girdle 12 and a pyramidal base 13. The girdle 12 has three sides which are initially bowed or convexly curved. Two mutually angled major facets 14 are polished on each side of the girdle in planes which are substantially normal to the plane of the table 11. Each corner of the girdle 12 between adjacent sides thereof has a corner facet 15 which is polished thereon in a plane normal to the plane of the table. The base faces 16 of thq pyramidal base of the stone are polished to an angle such that the angle-between each face and the plane containing the table is 25° to 40° so that a light ray 120 (Figure 6) entering the table 11 substantially normal thereto is reflected internally at face 16 to the opposite corner 121 where a multiplicity of total internal reflections take place to produce a finally reflected ray 122 which is again incident upon the face 16 for internal reflection thereat; the reflected ray 123 leaving the table or the faceted edge of the table.

The forming of facets on the girdle also enables additional light reflecting facets to be polished on the base and on the portion between the table and the girdle; as can be seen in Figure 1, the table is flanked with nine stars 17, six top corners 18, and eighteen halves 19 polished between the table and girdle per se. The pyramidal base of - 5 42227 the stone may have one cullet 20 comprising twelve bottom corners 21 and twelve halves 22. In a typical stone polished in accordance with the present.invention 68 facets are formed on the stone.

The polished stone has a high degree of light reflectance .5 and minimises the amount of material which must be removed from a rough made stone in order to achieve the required critical angle for such reflectance as compared with previous methods of polishing made diamonds.

The method of polishing gemstones in accordance with the 10 present invention is not only applicable to the polishing Of diamonds.

The essential feature is that the angle^i, see Figure 4, between the plane of each face 16 and the plane of the table 11 is such that internal reflections occur in the corner opposite the particular face 16 at which initial reflection takes place, in the case of Figure 4 indicated generally at 30.

Made stones polished in accordance with the present invention have been found to exhibit improved brilliance and larger stones have been.cut than has hitherto been possible.

Claims (24)

1. CLAIMS :1. A method of polishing a gemstone, which method comprises forming a table, a girdle having a periphery greater than the periphery of the table to define an intermediate portion therebetween, and a base extending from the opposite side of the girdle from the intermediate portion, polishing an odd number of converging faces on the base and forming a plurality of facets on the girdle of the stone, the inclination of the faces with respect to the table being such that light entering the table substantially normal thereto is internally reflected at a said face to a corner opposite thereto where it is internally reflected back to the said face and thence out of the table to impart brilliance to the stone.

2. A method as claimed in Claim 1 wherein the gemstone is a diamond.

3. A method as claimed in Claim 2 wherein the diamond is a made diamond.

4. A method as claimed in any one of the preceding claims wherein the gemstone is a relatively flat stone and is polished with three said faces on said base.

5. A method as claimed in Claim 4 wherein each said face is convexly faceted to assist reflection of the face towards the opposite corner.

6. A method as claimed in any one of the preceding claims wherein facets are polished on the stone about the girdle thereof between the table and the base in planes substantially perpendicular to the plane of the table surface. - 7 42227

7. A method as claimed in Claim 6 wherein the: gemstone is a diamond and the angle between the planes of the said faces and the table is within the range of 25° to 40°.

8. A method as claimed in any one of the preceding claims 5 wherein the said faces converge to a point.

9. A method as claimed in any one of Claims 1 to 7 wherein the said faces converge to a truncated portion.

10. A method as claimed in any one of the Claims 1 or 4 to 9 wherein the gemstone is a made diamond and wherein the girdle has a 10 plurality of convex faces and two facets are polished on each convex face and a corner facet is polished.on each corner of the girdle between adjacent convex faces.

11. A method as claimed in any one of the preceding claims wherein facets are polished on the intermediate portion between the table and the 15 girdle and on the base faces of the stone.

12. A method as claimed in Claim 1 and substantially as herein described with reference to the accompanying drawings.

13. Gemstones whenever polished by the method claimed in any one of the preceding claims. 20

14. Diamonds whenever polished by the method claimed in any one of Claims 1 to 12..

15. A gemstone having a table, a girdle having a periphery greater than the periphery of the table to define an intermediate portion therebetween, and a base on the opposite side of the girdle from the 25 table portion, which base has an odd number of converging faces, the inclination of the planes of the faces to the plane of the table 8 4 2 3 2 7 permitting light entering the table substantially normal thereto to be internally reflected at one said face to a corner opposite thereto where it is internally reflected back to the said face and thence out of the table to impart brilliance to the stone.

16. A gemstone as claimed in Claim 15, wherein the gemstone is a diamond.

17. A gemstone as claimed in Claim 15 or Claim 16 wherein the gemstone is a made diamond.

18. A gemstone as claimed in any one of Claims 15 to 17 wherein the stone is a relatively flat stone having three said faces on said base.

19. A gemstone as claimed in Claim 18 wherein each said face is convexly faceted to assist reflection of that face towards the opposite corner.

20. A gemstone as claimed in any one of Claims 15 to 19 wherein the girdle is provided with a plurality of facets lying in planes substantially perpendicular to the plane of the table.

21. A gemstone as claimed in any one of Claims 15 to 20 wherein the gemstone is a diamond and the angle between the planes of the faces and the table is within the range of 25° to 40°.

22. A gemstone as claimed in any one of Claims 19 to 21 wherein the girdle has a plurality of convex faces and two facets polished on each convex face and a corner facet is polished on each corner of the girdle between adjacent convex faces.

23. A gemstone as claimed in Claim 22 wherein facets are polished on the portion between the table and the girdle and on the base faces of the stone. - 9 4 2 2 2 7

24. A gemstone substantially as herein described with reference ’ to and as illustrated in Figures 1 to 3, 4, 5 and 6 of the accompanying drawings.