Primary Test: This Chatham Created Opal is the most convincing lab grown opal you will encounter. The structure of the color patterns, as well as the colors themselves, are the closest material to emulate a natural opal we have seen to date. As with most lab grown opal material, the growth structure is the key to separation from the natural opal. As you will see below, the colors appear to occur as tube like structures extending into the opal. This is rather classic for lab created opals and is very rare to find in natural opals. Natural opal color is caused by diffraction of light off of the silicon spheres that make up the opal, but with the lab grown material the colors appear as tubes extending into the stone.
Another important issue is a cellular growth structure seen at 60x + magnification. As with the other Chatham Created Opal we have listed, this looks very similar to the hydrothermal growth structure we see with gemstones grown by that method. While we do not fully know the process by which the Chatham Opals are created, we have seen what we refer to as this cellular growth structure in high magnification in these Chatham Created Opals.
By using the images below the separation of the lab grown opal is fairly straight forward.
Secondary Tests: None needed.
Repair and Setting: As a true lab created opal the same care should be taken as would be with a natural opal. No heat, no ultrasonic and no cleaners.