CHAMELEON DIAMONDS

 

Most people know that you can cut a diamond to change its shape, its clarity, its carat weight and even to change its hue(s). However the stone's primary colour (yellow, green, pink, purple, white, etc.) cannot be changed. At least not from cutting the stone. There is however a little miracle within these little miracles known as the "Chameleon Diamond". As you may have guessed from its name, these are diamonds that can in fact change colour.

The rarity of Chameleon diamonds and their interest for the connoisseur are due to their unusual ability to change colour temporarily when heated to about 150°C (“thermochromism”) or after prolonged storage in the dark (“photochroism”).

The stable colour shown by Chameleon diamonds is typically grayish yellowish green to grayish greenish yellow (as in "Figure 1"), while the unstable hue is generally a more intense brownish or orangy yellow to yellow (as in "Figure 2"). After heating, the colour of a Chameleon diamond quickly returns to its stable hue.

 

The colour change after storage in the dark is usually not as dramatic as that seen on heating. Some of these Chameleons have a stable colour reminiscent of “normal” green diamonds. While the green colour of these diamonds is caused by exposure to radiation, the mechanism behind Chameleon coloration is not yet well understood. Nevertheless, Chameleons are among the few green diamonds that can be conclusively identified as natural colour, since this behavior cannot be created or enhanced in the laboratory.

Relatively little has been written about Chameleon diamonds, and the precise definition of this behavior is not at all clear. For some members of the trade, a temporary photochromic colour change must be present for a diamond to be referred to as “Chameleon”; in contrast, many publications describe Chameleon diamonds as having either a thermochromic (using rather low annealing temperatures) or photochromic temporary colour change.

Chameleon diamonds were first documented in 1943 (GIA Diamond Dictionary, 1993), and since then they have been described in several brief reports. Extensive research on a single large Chameleon diamond was published by E. Fritsch and colleagues (1995). Most recently, Shigley et al. (2004) reported additional data on Chameleon diamonds, including the presence of Ni-related emissions detected by photoluminescence spectroscopy. We believe the past, present and ongoing research by EGL USA in collaboration with other gemological laboratories and universities worldwide is some of the most in depth studying being done regarding Chameleon diamonds. That includes an extensive report done on 39 Chameleon diamonds, from which much of the information herein has been collected.

 

 

There are actually two types of Chameleon coloured diamonds - Classic Chameleon & Reverse Chameleon.

Classic Chameleon coloured diamonds possess two very distinct natural capabilities. Classic Chameleon diamonds follow the thermochromic and photochromic behavior patterns as described above.

Reverse Chameleon coloured diamonds act almost exactly opposite to the Classic Chameleon diamonds. Reverse Chameleon diamonds have a darker stable colour. Its photochromic behavior enables the stone to temporarily change to a lighter colour when stored in a dark place for a longer period of time. When the stone is exposed to light, the darker colour is gradually restored. The other difference is that Reverse Chameleon diamonds do not have any reaction to temperature changes.

There are a number of characteristics that are common with all Chameleon coloured diamonds. First, they don't appear in all colour intensities. For example, they cannot be found with vivid and intense colours. Chameleon diamonds always possesses diamond Fluorescence and they will always include some sort of colour combination including any of the following colours: Yellow, Green, Gray, and Brown. This phenomenon cannot be found in pure coloured diamonds and most often contains at least two overtone colours. However, there a number of stones that contains only one secondary hue. Depending on whether the stones are Classic or Reverse, the dominant colour can be any of the four colors mentioned. Some of the more common overtone combinations are Brownish-Yellowish, Gray-Yellowish, Grayish-Yellowish, Gray-Greenish, Brownish-Greenish, and Green-Yellow.



With the wide variety of colours you can find Chameleon diamonds in, Chameleon diamonds have actually been classified as a natural colour of their own. Their behavior cannot be replicated and there is no known treatment to cause the Chameleon affect on other stones.

The colour of a diamond is created by the compound elements absorbed into the composition throughout its creation. Through the study of spectroscopy the various elements present in the composite of the diamond are defined. Even today, there is no known constant definition of elements present in Chameleon coloured diamonds.

The larger the diamond is, the easier it will be to identify the difference in colour variations. However, since these stones are so rare, finding a large Chameleon diamond is not exactly common place. As a result of their rarity, Chameleon diamonds are extremely sought after fancy coloured diamonds and are often sold for quite a hefty price.