Seeing is believing: what stone enhancements are acceptable? – by Christa Van Eerde (The Jewellery Editor – March 12, 2019)

The aim of this article is to explain the most common enhancements or treatments for the ‘big three’, which are acceptable and within what parameters.

Most of the ‘big three’ gemstones – emeralds, rubies and sapphires – are in some way enhanced or treated. Only the very pure, perfectly coloured and flawless can escape any type of enhancement, and this is reflected in their record-breaking prices. Perfection comes at a cost; the most valuable untreated ruby, the 25.59-carat Sunrise Ruby (below) fetched $30.3 million, which is just over $1 million per carat at Sotheby’s in Geneva in May 2015, far outstripping any price paid for a colourless diamond.

The same is true for top quality emeralds and sapphires, the more naturally perfect, the more valuable. But as not every stone is perfect, I explore the range of treatments and within which parameters they are acceptable to make the right choice when buying an emerald, sapphire or ruby. As gem treatments vary considerably and though sellers are ethically obliged to disclose if a gemstone has been treated, here is my advice on red flags to look for when buying a gem.

Any man or machine improvement to a stone’s appearance or value is considered a gem treatment. When a gemstone comes out of the ground as a rough it will usually be cut and polished, and though this improves a stone’s sparkle and shine, neither is considered a gem treatment. The most common treatments for the ‘big three’ are surface modification, cavity and fracture-filling, heat treatment and lattice diffusion.

Of these, heating and oil-filling are the most widespread and when applied correctly and disclosed are acceptable enhancements. Surface modification is only acceptable if the extent of the enhancement is fully disclosed.

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