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Chameleon diamonds: How heat and darkness bring out the best in these colour-changing stones

Chameleon characteristics

Figure1Chameleon diamonds do not appear in all colour hues and cannot be found in intense and vivid colours. However, the colour combinations always include the following: green, yellow, brown, and grey. Further, they most often contain at least two overtone colours, such as ‘greyish-yellowish-green.’ It is rare for a chameleon diamond to have only one pure hue, although some are categorized as ‘light to fancy light yellow,’ becoming greenish-yellow after heating (i.e. one degree more intense).

Colour description

For years, GIA included “Known in the trade as chameleon diamond” on its reports for only those stones exhibiting a ‘green’ or ‘greenish’ component; chameleons that were a mixture of yellow, brown, and grey did not receive this distinction on reports.

More recently, however, we have seen reports in the Canadian market for stones graded as ‘fancy grey’ that received the chameleon designation (Figure 2, page 3). This suggests temporary colour change is more important than the actual colour in daylight, and corroborates findings reported in a 2005 article (Hainschwang et al.) that even diamonds lacking a green component can be called chameleon.

Based on our research, we propose that two different stable colour groups can be observed in chameleon diamonds:

  1. Green with a grey, brown, or yellow colour component (‘olive’); or yellow with green, brown, or grey modifying colours. Both these groups exhibit green-to-yellow behaviour with heating or after prolonged storage in the dark. This colour change is commonly associated with chameleon diamonds, and as such, they are referred to as ‘classic chameleons’ (Figure 3, page 4).
  2. Light yellow to yellow, with typically a greenish, greyish, or brownish component. These are referred to as ‘reverse chameleons,’ as they lack a photochromic colour change—that is, they become slightly yellower and more saturated only when heated.

Similar to all fancy coloured diamonds, no two chameleons are exactly alike and many colour combinations are found.

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