Ring – Amethyst & Diamond
A bespoke made ring featuring a precision cut¹ amethyst in an asymmetrical diamond-tipped claw setting, surmounting a grain-set diamond collar and joined with a yellow gold ring shank. Circa 2019.
Assessment of the Amethyst.
Cut: modified round brilliant-cut (“Pseudo 11 Main Round Brilliant”, designed by Robert Long and Norman Steele², circa 1983).
Measuring: 12.42mm x 12.29mm x 8.13mm.
Weight (stone weighed loose): 5.85cts.
Colour: moderate reddish purple (10P.6/5).
Assessment of the Diamonds (20).
Diamonds in the claw tips.
Graduating in size: 0.90mm to 1.00mm.
Diamonds in the collar.
Average measurement: 1.20mm.
Total weight (stones weighed loose): 0.12cts.
Details of the Setting.
Hallmarked: 18ct gold, Birmingham convention mark.
Sponsor’s mark: ‘EV’ (Envi Jewellery).
Marked: ‘Au 750 CJ’.
Finger size: M.
¹. Gemstones are fashioned by way of cutting facets (flat surfaces). In the majority of cases the accuracy and precision of faceting, along with the quality of surface polish are regarded as less important – instead being cut to retain as much weight as possible. This result never makes the most of the unique optical properties a gemstone. Much light entering the gemstone is instantly lost out of the back (‘windowing’), or completely absorbed (extinction).
‘Precision cuts’ (sometimes called designer cuts) describe stones produced by cutters who employ highly specialised equipment which allows for assured repeatability, precision, and accuracy. The process of obtaining a highly flat facet requires the cutter to return to each facet time and time again, with ever finer cutting laps – consequentially each facet may be cut, and then re-cut between four and ten times. A finely cut facet improves the quantity and sharpness of light. The quality of light is further enhanced by close attention to the particular optical properties inherent to the nature of the material being cut – these facets are optimally angled for reflection. Such techniques allow cutters to produce designs which are unavailable from traditional techniques; superlative gems, some with unusual facet designs, or unique face up patterns.
². Robert Long was an engineer with Boeing in the 1950s, and worked on the Saturn 5 space mission in the 1960s. This background in precision lead him to the development of a pioneering faceting technique in the 1970s – ‘meet point’ faceting. Placing a sequence of facets on a gemstone is not a straightforward task. However, with the assistance of Norman Steel, a fellow Boeing computer programmer and interested mineral scientist, they applied three-dimensional geometry to exactly this problem. The outcome was special technique that allowed a cutter to approach a facet design and follow a disciplined set of instruction to exactly reduce a design, correct to a hundredth of a degree and without having to rely on direct measurement. The ‘meet point’ in the name is in reference to the apex, or junction, of three or more simultaneous intersections of facets; an essential element to the technique. This attention to details directly inspired faceting machine manufacturers to refine their products and improve the quality of materials and accuracy. Long and Steele produced a series of revolutionary books in faceting and are jointly regarded as leading proponents of precision cutting.