You're all familiar with the D-Z color grading scale, invented by the GIA deacades ago right? Well beyond the grade of Z, diamonds can still increase in yellow saturation, thereby extending their grade into the 'fancy colored diamond scale'. The prices of diamonds on this scale increase as more color is notably present.
Very intense examples of yellow colored diamonds are called canary yellows. These stones, if natural and untreated, can fetch up to thousands of dollars per carat on the international trading circuits.
Yellow fancy colored diamonds are much more affordable compared to other diamond colors- such as fancy pinks and blues. This is because they are the most common type of color that can be found in the gem species, along with browns, whites and grays. The best quality yellow diamonds however, provide a remarkably scintillating contrast in fine jewelry, especially when set against other pastel colored diamonds in a multicolored suite.
Diamonds that are yellow gain their color from nitrogen. A very small number of carbon atoms in the diamond's crystal lattice is replaced with nitrogen atoms instead, causing the yellow hues to arise. The quantity and grouping of these nitrogen atoms determines diamond "type" as well, which gemologists can also use in determining the natural authenticity of stones.
The fancy color scale for yellow actually considers stones in the X-Y-Z range of the normal scale as well. Both scales seemingly overlap, but the boundaries and acceptance of this merger is not always accepted by diamond dealers and buyers.
The scale for yellow stones goes from: Light (X-Y-Z range), Fancy Light, Fancy, Fancy Intense, Fancy Vivid, to Fancy Deep. The grades themselves are termed as phrases rather than letters. A last grade, "Fancy Dark" also exists, but does not necessarily function as a superior grade to fancy deep, merely a darker toned variant grade.
Many fancy yellow diamonds may also have a secondary or modifying hue. They can be greenish yellow or orangey yellow for example, which also factors in with the price calculations of a stone.
