The exposure of a gem to high temperatures for the purpose of altering its colour and/or clarity.

A chemical used to alter / reduce a component of, or the entire colour, of a porous gem. Some gemstones are bleached and then dyed, a form of “combination treatment.”

Altering a gem’s appearance by applying a colouring agent like paint to the back surfaces of gems (a treatment known as “backing”), or paint applied as a coating to all or a portion of a gemstone’s surface with the effect of altering the colour.

Introducing coloured dyes into porous or fractured gems to change their colour.

Filling surface-reaching fractures or cavities with a glass, resin, wax or oil to conceal their visibility and to improve the apparent clarity of gem materials, appearance, stability, or in extreme cases—to add to a slight amount of weight to a gem.

Heating a diamond to high temperatures under high confining pressures to remove, or change its colour.

The surface of a porous gemstone is permeated with a polymer, wax or plastic to give it greater durability and improve its appearance.

Exposure of a gem to an artificial source of radiation to change its colour.

This involves using a narrow focused beam of laser light to burn an open channel from the surface of a diamond to reach dark inclusions.

The penetration of certain elements into the atomic lattice of a gemstone during heat treatment, with the objective of changing or accentuating its colour.