New Article - A Study of Colored Stone Cutting Angles

. When asked to talk in Antwerp, I was delighted to find that the group was a gemological club, interested in colored-stones as well as diamonds. For the first time I was able to share these results with a broad-based audience and so I created this group of papers.

. Most colored-stone people are not interested in the 3rd section, but it is a part of the big picture; it verifies, by its extensive 3-D analysis of diamonds, the results found by my simple 2-D study which can be applied to all transparent gem materials.

.The "Faceting Limits" diagrams here are a simplified version of the original GIA article (1975) showing only the points of interest here; they do not include the head-obstruction zone for bezel-to-bezel rays, which rarely occur in stones of 'normal' proportions, and some of the lesser criteria.

. Andrychuk, also a mechanical engineer and faceter, had the same suspicion as I, regarding 'best slopes' versus RI, but lost his way in the forest and ended-up recommending cuts that had the viewer seeing himself! At the end of his book (1976) he acknowledges this, never having explained the trend or why RI 1.6-1.7 deviate from it. I am proud to have found both but was puzzled to note that the historically 'best' cuts were on the edges of the head-obstruction zone; 25 years later Garry Holloway explained that.

Bruce L. Harding, West Brookfield, Massachusetts, USA, 2011 Jan 28