Diamond grading is based upon a minimum of four criteria of quality. Cut, clarity, color and carat weight. Important also is the certificate that comes with each diamond.
A certificate should show the quality of the various criteria, for example the brilliance of a diamond is dependent largely on the cut of the diamond. A Princess cut (square cut) will produce much more brilliance than an oval or round cut.
Actually, many people confuse the diamond shape with the ‘cut’. The shape refers to the general appearance of the stone, emerald, round, pear, princess for example. The cut refers to the reflective qualities of the diamond. Even many jewelers do not seem aware of that. The ‘cut’ is what gives the brilliance factor to the diamond.
Diamond clarity is also very important. Very few diamonds are completely clear. Almost all will have some inner flaws or inclusions that have been created during the original forming on the diamond. The number size and amount of the inclusions is what determines it’s clarity. The less flaws and inclusion a diamond has the better its reflective qualities and the better its brilliance.
The diamonds color is also important. Actually the less color a diamond has the more desirable it is because it allows the most refraction of light. Color in a diamond reflect less light and so has less sparkle.
This does not apply to fancy colored diamonds which are extremely rare and can be any color from blue to green to bright yellow.
The carat is the unit of weight by which a diamond is measured. Larger diamonds are rarer than smaller ones so the value of a diamond rises exponentially with regard to its size and weight, all other factors above being taken into consideration also.
A diamond certificate is probably the fifth most important factor when buying a diamond and when checking the grade of a diamond. You should have as certificate from a recognized independent laboratory such as you will find in the appraisal links on the right.
Gaining an understanding of the above and really going through the information in this web site will give you a really good understanding of the importance of diamond grading.