Below are a few factors that reduce the value of diamonds.
The value of a diamond is determined by how colorless it is. Hence, the diamonds with a slight yellowish tint will always cost lesser than one that is clearer. This is because the presence of a yellowish tint will reduce the color grade of the diamond. However, that is a plus for budget shoppers as the yellow tint can be easily reduced by setting the diamond in yellow gold. This way, the color of gold will blend with the yellowish tint of the diamond, and hence, make the stone look whiter.
The proportions and geometry of cut in a diamond are very important as it directly affects the amount of light passing through it. For instance, a round cut diamond, which has been cut too shallow or too deep, will leak the majority of light passing through it. This will lead to a reduction in the brilliance of the diamond; the lesser the sparkle and shine of the diamond, the lower its price will be.