A large proportion of emeralds on the market today have been subjected to some kind of treatment process in order to improve their colour or clarity or both. The most common of these treatments is ‘oiling’. This involves filling the cracks in emerald with oil, a process which is carried out under vacuum. The oil is designed to disguise the cracks and to improve the way the stone looks. Whilst most producers of emerald consider this treatment to be normal practice, the oil does tend to dry out over time, leaving behind rather obvious looking pale fractures. Detecting the oil can be difficult. A microscope will often be needed to study any cracks for gaps that the oil has missed. Sometimes flashes of different coloured light will give away the difference in refraction of the oil and the actual emerald.
Another treatment that is even harder to detect is the use of polymers to fill fractures. The resin can appear so similar to the emerald that extremely careful observation is required to spot it. Again, flashes of light of different colours reflecting from the fractures may be a giveaway, and sometimes one can even see small air bubbles trapped within the resin. If the price of an emerald on offer seems a little bit too good to be true, then chances are it has been treated quite heavily.
It is worth mentioning here that extreme care should be taken when cleaning emeralds. They should never be placed in an ultrasonic cleaner in case the oils are washed out, and care should be taken with any kind of chemical cleaning fluid. Some unlucky people have been rather upset to discover that the deep green emerald they placed into an ultrasonic machine has come out looking like a shadow of its former self! With the oils washed out the stone has become a pale green stone full of cracks.
Aside from natural, treated emeralds, there is also an abundance of synthetic, man made emeralds on the market, as well as a whole host of other minerals used to imitate emerald. These stones, however, will have to be the topic of another blog.
If you have any emeralds that you wish to have valued then please contact Simon Rufus of Grand Auctions, Folkestone, Kent.