There are many aspects of a finished diamond that are dependent on the diamond cut, and one should be somewhat familiar with these. The most important of these include: brilliance, fire, number of facets or proportion, symmetry, polish, desired weight, and the diamond's final shape.

The cut of a diamond is, to be blunt, the approach and results of cutting the raw, rough diamond into the polished, shining stone that most of us are familiar with. More specifically, cut refers to the effectiveness of a diamond in reflecting and refracting light.

Proportion: The proportions of a diamond include the number of facets cut into the diamond, the size of the facets, and the length and width of the diamond. The ideal cut of a round brilliant cut diamond was first established by Marcel Tolkowsky at the beginning of the 20th century. For example, a diamond that is wide, but not deep enough in relation to its width at the girdle or table, will leak light out of the bottom (or culet) of the stone. On the other hand, a diamond with too deep, or long a cut, in relation to it's width, will leak light out of its sides. A diamond with the correct proportions will better allow light to pass unimpeded back to the eye, with its full color spectrum intact.

The ideal cut was designed to provide standard, mathematically accurate ratios of table size (the top, and largest facet of a stone), diameter (the diamond's width at the girdle), crown (the diamond from the girdle up), pavilion (the diamond from the girdle down), culet (the bottom, and smallest, facet of a diamond), girdle (the belt at the widest portion of the diamond) and depth (the entire diamond height from table to culet or top to bottom).

Polish: The polish of a diamond is fairly self-explanatory, in that it is the finished polish on a diamond's surfaces, or facets. The facets must have a good polish in order to most effectively reflect light that passes over the diamond. A poorly polished facet or facets can prevent a diamond from not only failing to properly reflect the light that is flashing over it, thus creating a dulled surface look, but poor polish can also cause a diamond to be diminished in its ability to allow light to pass into and through it, thus diminishing its fire and brilliance. In effect, a poor polish can ruin an otherwise spectacular diamond. A diamond's polish should produce smooth, clean and flat surfaces, so that the diamond's play of light is utilized to its greatest effect.

Symmetry: The term symmetry refers to the placement of a diamond's facets. The facets themselves are the flat surfaces that we are familiar with when we think of a diamond. These surfaces must be aligned in just the right orientation to one another, and they must be sized in relation to one another. If a diamond has proper symmetry, this indicates that its facets are all the proper size in relation to one another, and that there are the proper number of facets, in relation to the size and desired effect of the diamond.

Good symmetry provides the kind of light reflection that produces the dazzling light display that we know as "scintillation". It is these scintillating flashes of light that most of us think of when we think of the perfect diamond. A diamond with poorly aligned facets will have poor symmetry, and will not provide the kind of bright flashes of reflecting light that most of us would desire from a diamond.

Weight: In the case of such diamonds, the rough diamond is cut to best accentuate the particular qualities of the diamond. For example, a diamond may be cut for greater depth, or greater width, so as to allow for a larger carat weight. While these diamonds may not have the brilliance or fire of an ideal cut diamond, their weight allows them to have greater value than they would otherwise have should they be cut down to an insignificant size for the sake of an ideal cut.

The desire for a particular carat weight also comes into play in the choice of cut for a diamond. While the ideal cut may seem to be what is desired above all, this is not actually the case. There are many rough diamonds that, due to various reasons such as cleavage points, and inclusions, would be diminished to insignificant carat weights should they be cut to ideal proportions.

Shape: When a diamond is cut, the diamond will have a particular shape. This shape is usually determined by the motivation of the cutter, to supply the largest and best quality diamond; which means he must follow the structure of the diamond's original rough. There are numerous shapes for diamonds, with no particular shape being better than any other, although the current market demand is for round brilliant and princess cut diamonds. However, keep in mind the shape of a diamond that is right for one person may not be right for another.

Brilliance: The brilliance of a diamond is a direct result of a diamond's cut. Brilliance itself is simply what is implied in the word; the brilliant shine of light that a particular diamond is able to reflect and refract. A high brilliance tends to be the main goal of a diamond cutters art, as a brilliant stone is often regarded as the most desirable of diamonds.

The ideal cut was meant to provide a cut that maximized the potential brilliance, or light producing qualities of a particular diamond. Essentially, light that passes through a diamond that is cut well will allow more of the light to come back out of the crown, or top, from which it entered, with the entire color spectrum intact.

The intact color spectrum is the internal brilliance that we see when we are looking at a diamond with a good cut as the light is passing through it. The light that does not pass through the diamond, the reflected light, is its luster, or external brilliance, and is the result of the light reflecting off of the diamond's facets. The white light that is known as brilliance is a result of the pavilion's cut.

Fire: Fire, like brilliance, is a description of the light qualities of a diamond. In the case of Fire, however, the light quality that is being described is the amount of light that is seen to be emanating from the center of the diamond. Fire is a descriptive term used to illustrate the colorful splash of light that the light passing through a diamond produces in the center of the diamond itself.

As with the light properties involved with brilliance, fire is the result of light being split apart into its color spectrum within the diamond, whereas brilliance comes from the intact color spectrum coming out of the diamond. Fire is what is seen of the color spectrum of light as it is broken up into its various bands while still within the diamond. The full spectrum color that is known as fire is the result of the cut of the crown.

To save some money without affecting the beauty of the diamond it is wise to look for diamonds that fall just outside of the "ideal cut" parameters. To the unaided eye, a diamond of less than ideal proportions can look just as good as an ideal cut.

Once a diamond is set, any differences between a good, very good and an ideal cut diamond are often lost to the untrained eye. Also, a diamond that is not ideal proportions can have a lower depth % in relation to its width, and will actually make the diamond appear to be larger than its ideal cut counterparts. It is in this way that a small stone can be made to appear to be much larger and save you money.

There are also those who have come to regard the Sarin report as a superior determinant in the quality of a diamond. Thinking in this manner will only cause you to spend more money than is necessary. The Sarin machine measures the actual proportions and dimensions of a diamond, and this measurement is placed against the ideal cut ratios and measurements. Again, while the Sarin report can give you an accurate reading of the diamond in question, it does not mean that you will ever be able to see the difference between a very good or good diamond, as compared to the measurements for an ideal cut diamond.