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Brown Champagne Diamonds
Brown diamonds are located close to the lower end of the value scale for several reasons. One of the reasons is that the colour brown is not considered as glamorous and desirable as some of the other fancy colours. Another reason for the lower price is the fact that the supply of brown rough is quite abundant, which means that supply is less of a factor in determining price or desirability. However, large brown diamonds that receive a high clarity grade or contain orange of pink modifiers are considered more valuable than regular brown diamonds.
What makes a diamond brown?
Brown colours are caused by dislocation within the crystal structure, known as ‘plastic deformation’. This occurs when growing pressures within the earth create a movement within the crystal structure that deforms the crystal structure from its regular pattern and introduces vibronic colour centres with unbonded electrons. Brown can also be caused by hydrogen, nitrogen and nickel defects within the structure. These may show absorption lines at 503nm and 494nm of varying intensity. Visually, this plastic deformation is the cause of the graining seen within brown diamonds.
Plastic deformation (change in the diamond's molecular structure) creates the brown colour in diamonds. These brown coloured stones generally contain lower levels of nitrogen (which causes the yellow colouring) than other diamonds, making them more susceptible to deformation. Brown diamonds that are light in colour are sometimes referred to as champagne diamonds, whereas browns that contain a significant amount of orange mixed with a dark brown hue are called cognacs.
While browns are considered one of the most affordable of all fancy colour diamonds, it is relatively rare to find a diamond with a report stating that it is pure brown (a fancy brown without a secondary colour). One reason for the few reports may be the low demand for certified brown diamonds. Dealers sometimes refer to brown diamonds as TLB or 'Top Light brown’. They are actually referring to light brown diamonds that appear almost white when facing up. This applies to round diamonds only.