To bring out the beauty of a diamond, a number of additional processes are necessary. These processes, which include cleaving, sawing, cutting and polishing, are usually known collectively as diamond cutting and are the most exacting and difficult techniques of lapidary art. The primary object of diamond cutting is to bring out the fire and brilliance of the stone. Equally important, however, is the cutting of the stone according to a plan that will eliminate imperfections such as cracks, flaws, and cloudiness. This plan will produce a gem of the greatest size , best appearance, and therefore the maximum value. The term "cut" refers to the proportions of a diamond.

In 1919, a mathematician from London, Marcel Tolkowsky, calculated and published the proper proportions for maximum brilliancy with maximum dispersion from a round brilliant cut diamond. This became known as the "Tolkowsky Cut". Because many people could not pronounce or spell his name, and they considered his calculations to be the ideal cut, soon it was called the "Ideal Cut".

The "Ideal Cut" has some problems however. It yields the smallest weight retained from rough diamond. Diamonds with these proportions are rarely cut today. The weight loss from the rough is too great, and the price of the diamond is too high. One diamond company cut and sold "Ideal Cut" diamonds only, and recently they filed for bankruptcy. The public will not pay for the lost weight, and they have a taste for a table larger than 53%. Most diamond cutters and dealers agree that 58% is the optimum, and many larger tables are accepted.

There are pros and cons to proportions. For example, if the table is slightly spread, then the total depth percentage will be lower. The spread table makes the crown height lower. This is good for people who want a larger stone than they can afford. The spread table will make the diamond have a larger diameter, and it will look larger than it really is. If the depth percentage is much over 62% or much less than 57%, then the diamond begins to loose light through the pavilion. This results in a less brilliant stone which should be cheaper than a bright one.