Fancy-Coloured Sapphires: Why Corundum Is Not Always Blue

Sapphire is often associated with blue, but the corundum family offers a much broader colour range. Yellow, pink, violet and green sapphires are examples of the fancy colours discussed in SSEF’s 2012 Facette. A colourless ideal composition can become colourful through very small changes.

What produces the colours?

Pure corundum is aluminium oxide. Small amounts of other elements can enter its crystal structure and change which wavelengths it absorbs. Chromium contributes to red ruby colour, while iron and titanium are important in many blue sapphires.

The colour depends on more than the total amount of one element. Its chemical state, combinations with other elements and colour centres in the crystal can all matter. Some corundum also shows different colours or shades in different viewing directions, a property called pleochroism.

Why colour names have boundaries

SSEF discusses the difficulty of separating nearby colour categories, such as pink sapphire and ruby. Variety names involve accepted definitions, not just poetic descriptions. A seller’s colour word should be read alongside the laboratory’s identification.

Natural colour is a separate question

A pink or yellow sapphire may have its own treatment history. Neither the hue nor an attractive photograph proves that it is untreated. Ask for a clear treatment statement. This post explains the science in the 2012 article and does not turn its historical demand observations into a claim about the current market.

Sources and further reading

SSEF Swiss Gemmological Institute, Facette, issue 19, January 2012, pp. 6-7, “Fancy-coloured sapphires: classical gemstones with a rich colour spectrum”. Read the original SSEF PDF.

This independent educational article explains historical SSEF research in original, simple English. It is not an SSEF publication. No source photographs or illustrations are reproduced.