Sizes gems

Most rough gemstones require cutting and polishing to unlock the colour and lustre for which they are known. This is the job of the lapidary.

The earliest method of fashioning gems was simply to polish the flat crystal faces developed by nature. This later gave way to the cabachon, a style of cut imparting a curved upper surface. This is a French term which itself was derived from the Latin cabo, meaning head. Still in use today, the cabachon cut is used for star or cat’s eye gems. The cabachon may be cut in a number of ways. Domes vary from low, almost flat surfaces, through high, steeply curved surfaces. Usually a medium to high dome is preferable. The symmetry of the top and bottom surfaces on cabochons, and also nicely bevelled edges are criterions for a good cut. In cutting star material, orientation is all important, for, if done improperly, the star will be off-centre or nonexistent.

Only in the second half of the second millennium did we have the development of the faceted cut. Faceting, which produce scintillation in addition to colour, came into vogue with a technical improvement due to appearance of grindstones. Grindstone has permit to add some new facets to the natural ones. Faceting is a technique which requires a lot of experience. The shape, proportions and orientation of the stone being determinant for its final value.

Corrrespondences between size in centimeter and weight in carat
size (in cm)	0,6	0,8	1	1,2	1,5	2	2,5	3
Cut stone (in ct)	1,5	2,5	4,5	6	9	18	30	45
Cabochon (in ct)	2	3	7	9	13	25	35	50