Trade Alert: Diffusion Treated Corundum

A quick alert. The U.K. jewellery trade has recently been targeted by unscrupulous gem dealers passing of lattice diffused corundums, particularly blue sapphires. This is the perfect example of manufacturers buyers getting too comfortable. Keep alert. Diffusion treatments produce colours that are too good to be true. When was the last time you had your pick of fine colour sapphires? They are still hard to come by. If you employ gemmologists or people with gemmological training, get them earning their pay and saving you from costly litigation. These treatments are usually easy to spot with a microscope, methelene iodide immersion liquid, darkfield lighting and patience. This treatment penetrates to a maximum depth of 0.5mm, usually alot less, as this would mean a longer treatment and more money is spent. Look out for lighter colour facet junctions and pitted girdles. Because the treatment is shallow, it needs to be perform on pre-cut stones. The excessive heat, effectively melts the surface, meaning it has to be repolished. Facet junctions receive more polishing, therefore the treatment is removed from there first. Most lapidaries working on these treated stones are too lazy to polish girdles again, leaving behind the altered surface. If you need further information there are plenty of sources. In particular I would refer you to www.ruby-sapphire.com where the great Richard Hughes has a an article titled "Vampire Blues". Please take note, as he suggests this is not new, just recycled. Take care Damian