50 shades of pink

This note is dedicated to diamonds, which have an unusual pink hue in their coloring. How to classify such stones is one of the pressing issues facing practicing gemologists.

In Russian legislative acts (GOST), a pink shade is not provided for in the list of ordinary colors, and the position of stones with a pink hue is also not fully defined in earlier documents, such as "technical specifications ..." (TU).

In foreign practice, the concept of equivalent colors is introduced for stones with non-characteristic colors. That is, unusual colors, such as pink, blue, green, purple, are considered according to a slightly different system, different from the classification of yellow stones. When evaluating such colors, "equivalent" colors serve as gradation, covering not a letter color interval, but a whole group of such intervals.

This is how the groups of colors "Faint color", "Very Light", "Light" are distinguished, which do not have the prefix "Fancy" ("Fancy"). Stones that have a more saturated color are fantasy and for them, the word "Fancy" ("Fancy") is added before describing the color, characterizing the saturation of the color. In the pink range of fantasy colors, the following degrees of coloring are distinguished – "Fancy Light ...", "Fancy ...", "Fancy Dark...", "Fancy Intense ...", "Fancy Deep ...", "Fancy Vivid...", "Fancy Red...". Stones of the last degree of gradation are the rarest in the group of pink-red stones.

But in addition to the rarity of color and the high cost of such stones, many pink stones stand out with one remarkable feature – they exhibit pleochroism, that is, depending on the position of the stone, it may have additional shades – orange or purple. The peculiarity of this behavior of a diamond, as an isotropic stone, is explained by the nature of the pink color in most stones. In addition to the fact that the symmetry of the defects causing the pink color in diamond is different from the cubic one, these color centers are oriented in the stone not chaotically, but in accordance with certain crystallographic directions. As a rule, such directions coincide with planes of plastic deformation or double seams, which causes the heterogeneity of the color created by them, depending on the orientation of the stone relative to the observer – perpendicular or parallel to such a plane.