Testing for chameleon diamonds
The characteristic ‘olive’ colour of chameleon diamonds may be deceiving. Our lab recently tested a 1.12-carat fancy greyish-greenish-yellow (‘olive’) diamond of I1 clarity and with typical strong orangey-yellow fluorescence similar to what chameleon diamonds can exhibit (Figure 4). However, this stone did not change colour when heated.
The following are simple ways for a jeweller or gemmologist to recognize classic chameleon diamonds:
- Visually inspect the diamond for a greenish colour modifier.
- Look for strong orangey-yellow fluorescence under long-wave UV light.
- Check for phosphorescence (i.e. a weak to medium greenish-yellow colour when short-wave UV light is removed).
Only when all these initial criteria are satisfied should the stone be gently heated on a hot plate to observe the colour changing from green (ish) to more orangey-yellow. (Note: If using a lighter, keep the diamond in motion over the flame. This test is not recommended for stones that are more green than yellow.) If the diamond is a chameleon, it will revert to its original body colour within a couple of seconds. (Place it on white paper to better observe the colour change.) It is advisable to send any natural olive-colour diamonds to a laboratory to confirm by advanced testing whether they are chameleon, as heat may change the colour of a non-chameleon green diamond permanently.
