Stone working – Precious stone working
Patent
1991-07-08
1993-03-02
Smith, James G.
Stone working
Precious stone working
51283R, 63 32, B28D 500
Patent
active
051900246
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a diamond sawing process, and in particular to a diamond sawing process for diamonds which are to be round cut.
Until the fourteenth century, although diamonds were worn in jewellery, they were uncut and worn primarily as amulets. A roughly-fashioned diamond has very little life or sparkle; only when the rough diamond is cut in a sophisticated manner does the life and sparkle become evident.
Cut diamonds appeared in European jewellery, initially as a table cut (FIG. 1), achieved by grinding off the tip (top corner) of a natural octahedron, the octahedron being one of the forms in which diamond crystals occur in nature; the table cut was also extensively used by the ancient Indian lapidaries, who had been faceting diamonds for generations when the European diamond cutters visited them in the seventeenth century.
Another cut employed by medieval lapidaries was the lozenge. This is obtained by grinding away one of the corners on the girdle (widest part) of the octahedron until what is commonly known as a "diamond-shape" is achieved; the result is attractive but a lot of material was wasted, and the cut was therefore not often used.
A popular cut is the "brilliant cut" (FIG. 2 and FIG. 3) in which fifty seven facets (and sometimes an additional culet facet at the bottom tip) are cut from an octahedron; the outline (plan view) of most modern brilliants is circular, but older stones were often "cushion-shaped" (squarish with rounded corners); the brilliant cut revealed for the first time the fire of the diamond i.e. the dispersion of light into the colours of the spectrum, intensified by increasing the length of the path the light travels within the stone, the facets being arranged so that the light is internally reflected from one facet to another so as to travel through as long a path as possible (with total internal reflection) before finally emerging from the stone. With the development of optical science, the cutting of "brilliants" has been improved, and numerous modifications have been introduced over the years to cope both with crystals of different shapes and with very large stones.
Although traditionally referred to as a "cut", usually the facets were ground off and the diamond dust lost. However, Loesser in his 1900 U.S. Pat. No. 671,831 proposed a sawing or cross-cutting process to cut a diamond in two, for the purpose of reducing diamonds to a better size for being worked up into brilliant shape; Loesser proposed removing the top tip (or a corner of the stone just above and parallel to the girdle) as a fragment which could be saved and fashioned into a small brilliant or other form. Loesser states that prior to his invention, in order to produce the flat table formed by the cross-cut, the stone had to be gradually and very slowly ground down, producing powder which flies into the air and is of no commercial value. Another disclosure of a cross-cut to both produce a table cut and a unitary fragment is the 1902 Schenck U.S. Pat. No. 732,119, with a special pre-notching to provide partially-cut facets.
We now propose a diamond cutting process in which a diamond of modified girdle shape, particularly a round cut diamond such as a brilliant, can be fashioned by sawing, with less wastage of material than in the processes of which we are aware.
Thus according to the invention we propose a diamond cutting process for a diamond having a girdle and a plurality of apices, which includes the step of removing an apex as a unitary fragment characterised by starting a cut to one side of the girdle and continuing it through the girdle to the other side of the girdle, whereby the fragment removed is a girdle apex. The process will usually be repeated for the other three girdle apices, but of course whether there are four girdle apices to be removed will depend both upon the shape of the individual crystal and the desired cut. The top and bottom tips can also subsequently be removed. The girdle apex fragments (and top tip and bottom tip fragments) can thereafter all be used for fashioning in
REFERENCES:
patent: 671830 (1901-04-01), Loesser
patent: 671831 (1901-04-01), Loesser
patent: 694215 (1902-02-01), Stuurman
patent: 732118 (1903-06-01), Schenck
patent: 732119 (1903-06-01), Schenck
patent: 3527198 (1970-09-01), Takaoka
patent: 4392476 (1983-07-01), Gresser et al.
Kasper Horst M.
Smith James G.
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