Symmetry
Fancy Cut Diamonds
Light travels through a fancy cut diamond the same way as through a round brilliant, but different shapes result in the need for different proportions. While there are no specific ideal dimensions in fancy cuts unlike in round, there are still some rules that make fancy cut diamonds look better.
The same principles of optics and symmetry apply to all diamonds. In fancy cuts that are significantly longer than they are wide, the symmetry along the main axis is particularly important. It is also desireable that cuts such as marquise, oval and pear look somewhat round as opposed to square. An oval diamond should look like an elongated circle, and not like a rounded rectangle. Princess, cushion, asscher cut stones look best as perfect squares, when the length to width ratio is between 1 and 1.05. When this ratio is slightly over 1.05 the diamond will look off shape: not a perfect square and not a pronounced rectangle. Pear cut diamonds will look best at the length to width ratio of 1.5 to 1.75, while marquise shows its beauty best at the ratios 1.75 to 2.25.
It is worth noting that fancy shapes are very often used for fancy coloured diamonds. The reason is that while round brilliant is the cut that allows for maximum brilliance and brightness, other shapes are much better at showing off colour. They will often be cut deeper in order to increase the distance that light travels inside the diamond and let it get a more saturated colour in the process.
