- (a) Gemstones may have been treated by heating (generally), or diffusion (sapphires) to enhance the colour of the stone.
- (b) Created gemstones are grown in strictly controlled laboratory conditions to recreate the brilliance of rare natural gemstones.
- (c) Black diamonds are enhanced by high temperature to permanently create the intense black colour.
- (d) Blue, yellow and red coloured diamonds have been irradiated to achieve their colour. Colour treatments used on diamonds may be sensitive to high temperatures and heat.
- (e) Enhanced blue turquoise stones are treated with a dye to enhance the natural blue colour.