Pink diamonds are different from other fancy colours in that they do not get their colour from any trace element such as yellow and blue diamonds do. Instead, after their formation, these stones are subjected to very high temperature and non isotropic stress which deforms the crystal lattice and displaces some of the carbon atoms from their regular positions.
It is accepted today that these structural defects are the cause of a diamonds pink hue. In pink diamonds from the Argyle mine, these defects are very obvious and can be seen as “graining lines” with the help of a microscope and in some cases even apparent to the naked eye.
Like other colours GIA grades pink in terms of tone hue and saturation. As tone and saturation increase rarity goes up as well as value.
Starting from low tone and saturation and increasing GIA grades pink diamonds as light, fancy light, fancy, fancy intense/ fancy deep, and fancy vivid. Pink diamonds are unique in that when a stone falls into the rare category of extremely high tone and saturation GIA uses the term “fancy RED” to classify it.
Modifiers also exist in pink diamonds. These include brown, orange, and purple. A brown modifier exists when the saturation of the diamonds is not strong enough to overpower the tone.
As the brown in a pink diamond becomes more apparent the value of the diamonds is significantly reduced. Orange as a modifier is present when either the hue of the diamonds starts to lean towards orange or when the tone is starting to overpower the pink. Some orange-pink diamonds are very beautiful but because their colour is associated with brown the orange modifier also devalues pink diamonds.
Purple is the one modifier that does not significantly devalue a pink diamond. A premium is even added to the price for stones with noticeable purple hue.
The colour in purple-pink diamonds is caused by the grain lines displaying a different wave length in the colour spectrum.