Bulk diffusion or beryllium treatment is a new treatment that has only been known to the market for a short period of time. It is obvious now that this treatment has been experimented with for much longer but it is unknown how many gems entered the market before this treatment was disclosed - a practice still continuing today.
The initial version of this treatment was originally relatively easy to detect as a simple immersion test could detect the surface colouration induced by the treatment. However, more sophisticated versions of this diffusion treatment can induce colour throughout the entire gemstone and the presence of unnaturally high levels of beryllium can only be detected by very expensive chemical analysis. Currently, there is no practical detection method.
Although detection of this treatment is difficult, one thing to look for is evidence of very high temperature heating ( > 1800 °C) sometimes for extended periods. This does not prove that beryllium has been used but is indicative.
These treatments are extremely common in sapphire other than blue - you should assume that all yellows, oranges and padparascha colour sapphires have been treated in this way unless you have specific written documentation to say otherwise. Unfortunately, it is now clear that this type of treatment is also used to create a desirable colour of blue. Therefore, all buyers should demand written guarantee of treatment status before purchasing. Do not pay more for fine colour if this colour is not natural - this value is artificial so beware.
Reputable sellers will disclose this treatment using terms such as bulk diffusion, lattice diffusion, beryllium or Be treatment. Aussie Sapphire does not support the use of this type of treatment and do not treat any of our gems in this way.