Beryllium also known as Be treatment, bulk or lattice diffusion is a relatively new way for treating gemstones intended to intensify the colour of a stone. This is a form of heat treatment with the addition of beryllium to the heating process which results in a new colour. Unlike other methods this one allows the entire gemstone colouration, thus the stone can be recut in the future. Beryllium treatment is mainly applied to sapphire. Almost all sapphires of yellow and orange colour have been treated this way unless there is a written proof of its origin. Moreover, even a desirable colour of blue can produced today.

Sapphires heated with beryllium are extremely difficult to detect and require expensive chemical analysis. Although this technique is widely accepted as a legitimate type of gemstones treatment, sellers are expected to disclose it. Otherwise, buyers should not hesitate to ask for a written guarantee so as to find out whether the colour is natural or artificial.