Treatments to improve the gemstone quality
– Ruby before and after lead glass filling –
Since ancient times precious stones without excellent features, typical of best quality gemstones, used to undergo enhancement treatments to improve them. Pliny the Elder was the first to describe those techniques in his Historia Naturalis.
Today it should be compulsory to report which are the treatments the gemstones have undergone.
The international organisation that supervises the fine gemstones trade, highlights the need of total transparency in buying and selling and in the declaration of how many and what kind of treatments the gemstone has undergone.
This does not happen as many traders think it would cause clients’ mistrust and confusion for something that is actually very common.
They would be right if the appraisals of treated and un-treated gemstones were the same, but it is not the case. The price can vary substantially so it is important to analyse this aspect in order to make a good investment rather than buying something that is just pleasing to the eye.
Treated gemmiferous materials should be described in a gemmological certificate following this technical classification:
heated: materials that underwent a thermal treatment;
oiled: materials whose fractures have been filled with oils or other oily colourless liquids;
oiled with pigment: materials whose fractures have been filled with coloured oils or other oily liquids;
diffusion treated: materials that underwent a thermal-diffusion process with addiction of chromophore chemical elements.
Impregnation treated: materials whose pores have been filled with colourless substances
irradiated: materials whose colour was modified through invisible radiation or bombarded with atomic or sub-atomic particles.
Filled: materials whose cavities have been filled with fluid colourless or coloured substances that harden after application.
Coated: materials that have been totally or partially coated with other substances.
Dyed: materials whose pores, cavities and fractures have been filled with coloured substances.
One of the most common treatment for coloured gemstones is heating.
This treatment consists in heating gemstones at high temperatures (up to 3000 degrees): this process makes electrons move about within the crystal and improves the colour.
This treatment is very common for sapphires; in this case it does not reduce the price but it is a bonus for totally natural sapphires that are becoming rarer and rarer.
Almost 99% emeralds undergo oiling treatment in order to mask small surface fractures that are very common in these minerals.
Other treatments reduce gemstones price to 1/10th of its original value because the original material is very bad quality.
This often happens with rubies: as rubies are rare and very expensive, also the waste material is treated to make it fit for commercial purposes.
The treatment I am talking about is the filling of fractures with lead glass or flux which is possible to see a picture, at the topo of the article, of a ruby, before and after the treatment.