18K (750) white gold and platinum ring, featuring a rectangu - Lot 53

18K (750) white gold and platinum ring, featuring a rectangular cut emerald set with two rounded old-cut diamonds. French work of the 1940s. Finger size: 55. Emerald dimensions: 10.3 x 9.6 x 7.2 mm. Gross weight: 5.1 g (slight chipping) The emerald is accompanied by a GEM Paris report (2023) attesting: origin Colombia, modification by slight oil impregnation not significantly affecting the stone's appearance. Emeralds of this type are known as "Gota de aceite". GOTA DE ACEITE EMERALD The term gota de aceite, which can be translated as "drop of oil", is used for certain rare emeralds with a specific visual appearance: resembling honey or oil, they were first given this name by the Spanish conquistadors, because of this very appearance. It is important, however, not to confuse this effect with the presence or absence of oil. The term "oil" is used here to define the optical effect and not any treatment of the stone. The term gota de aceite first appeared in Gems & Gemology magazine in winter 1944-45. Since then, the phenomenon has been studied to determine its cause and location. Today, there seems to be a consensus that the gota de aceite effect is due to internal peculiarities of the emerald's crystal structure. This structure must be angular or hexagonal, but also transparent so that the play of light dispersion can emerge. In terms of provenance, a large number of emeralds with this effect come from Colombian mines, like the one shown here, but they can also be found in Brazil or Zambia.