Colour can dramatically influence the values of the other 3 C’s especially now that we know colours and synthetic stones can be controlled under certain conditions of high heat high pressure. HPHT. D-L refer to the whites and M-Z refer to the tinted colours.
The paper or card that the diamond is laid upon when its color is being checked is called coloured paper. When checking the color of a polished diamond, it is important that there are no ambient influences which might alter one’s impression of a diamond’s true colour, such as: the colour of the room, the work table, or even the clothes of the person checking the colour.
In order to prevent ambient colors from affecting the test, the diamond must be checked on a plain white background, with no gloss, and with no yellowish hues, close to a neon light bulb, filtering the spectrum of colors. The easiest way to achieve these conditions are to fold a piece of white paper into a ‘V’, with the diamond laying in the resulting crease, with the table facing down, and the inspector looking at the body of the diamond through its pavilion. The upper side of the folded piece of paper blocks the background colours and allows one to accurately observe the true colour of the diamond. To make sure that the diamond doesn’t fall off the paper, the paper is folded and the diamond is laid on the inner crease. If one wishes to achieve a highly accurate colour grading, a Master Stone is laid next to the diamond.
The colour paper or color card is especially important when inspecting large diamonds, and therefore all diamond dealers have these. Therefore, some use it for advertising purposes. The advert is printed on the outer sides, so that when the card is folded, it does not appear in the area that is used to inspect the diamond. It has turned into a kind of business card that is used to check for colour, and that’s why it is called a ‘colour card’.