Red diamonds with their stimulating colour are a metaphor to a deep passion. Technically speaking red diamonds are very highly saturated pinks. To be specific, the Gemological Institute of America assigns the colour Red only when saturation levels reach beyond 50%. Red diamonds are visually also darker toned than vivid and even many deep pink diamonds. Given that red is so rare and only covers a very narrow colour range, the GIA only assigns the grade ‘Fancy’. Exquisite Fancy Red Diamonds are among the rarest and certainly most highly quoted of all diamonds. Amongst red diamonds a pure Fancy Red is the most highly regarded, closely followed by a Fancy purplish Red which for its richness is much revered by some expert dealers. Orangy Red comes in third place and the far less attractive and commercially problematic brownish Red a distant last. Brown as a modifier, unfortunately, impedes the colour markedly.
Red diamonds, being the continuation of pink diamonds are classed as Type I diamonds in which severe plastic deformation – expressed as coloured ‘grain’ lines – is even more closely spaced than in their pink siblings. This characteristic graining moreover is coupled with vacancies associated with isolated nitrogen atoms. It thus comes as no surprise Red diamonds commonly feature dense tatami like stress related birefringence which poses an obvious risk during the manufacturing process.
Ming localities known to produce the occasional red stone include foremostly the Argyle mine in Australia, the Brazilian region of Minas Gerais with its many diamond bearing tributaries and the Kapuas River on the Indonesian island of Borneo.