EMERALDS

Emeralds are very beautiful when found in the highest grade of colour and are therefore highly prized and very rare. They are hard physically, yet quite brittle and subject to breakage if handled roughly.
They are usually enhanced by immersion in oil, such as cedar oil, and this is an old practice used for about 3000 years, and therefore not considered an enhancement as such.
Other treatments which are officially seen as enhancements include the use of resin which is injected under vacuum around the whole stone, so that as the air is withdrawn the resin seeps into any surface reaching cracks. BGI is equipped to detect such treatments.
There are even cases where a natural piece of emerald may be glued onto a section of quartz to simulate a natural stone, and this would be classed as a fake gemstone, and was quite widely practised in the 20th century. Such cases are now quite rarely found, but unless a gem is described as natural, it may not be entirely so. It is wise to check.