In the top left, you will see the GIA certificate number and the date the certificate was issued (see left). The GIA certificate number is a filing number for the GIA for the diamond indicated by the certificate. Every diamond that has been certified by GIA has it’s own unique number.
Sometimes this number is laser inscribed on the GIA certificate to help identify it, however this is not done to all diamonds. The date is the actual date the diamond was examined by the GIA laboratory.
The finish of the diamond indicates how well the cutter has aligned the facets and polished them. GIA grades finish in two catagories and uses the following grades;
• Very Good
The polish grade of the diamond reflects how well the cutter has polished each facet. One aspect of polish is the cutter leaving polish lines on the diamond. These are caused by the cutters wheel not having the proper amount of oil, or pressing the diamond against the wheel with too much pressure, and leaving visible lines on the facets of the stone. Another aspect of polish is surface graining.
Diamonds, much like wood have grains which the cutter comes across when cutting the diamond. The cutter taking great care when polishing the diamond can make these grains almost invisible, or being less careful can leave these grains obvious.
While most diamonds are graded Good in polish, grades of Very Good or Excellent can cost quite a bit more. Most consumers can not see (even under magnification) the difference between Good and Excellent polish. I would not recommend a diamond that is graded less than Good in polish. It is up to you to decide whether the pursuit of perfection is worth the added cost.
The symmetry grade of the diamond reflects how well the cutter has aligned each facet and how well the facets come together. The facets should come to perfect points and should point at each other correctly. You must bear in mind that the symmetry grade of the diamond only indicates meet point symmetry and does not reflect how well the diamond is actually proportioned.
Again I would not recommend a diamond that is graded less than Good in symmetry. Exactly like polish it is again up to you to decide if a grade of Excellent as opposed to Good is worth the added cost.
Color and Clarity
Also included on the GIA certificate are the color and clarity grade. These along with the carat weight are the primary factors in determining the price of the diamond.
• A place where GIA can note anything not covered in the rest of the certificate. Common comments here include characteristics not plotted and major symmetry issues. In the example above we see that pinpoints (small diamond inclusions) where not shown on the plot, and that the crown angles are greater than 35 degrees.
Crown angles greater than 35 degrees, and crown angles are less than 28 degrees are my two least favorite comments. By a cutter making the crown angles higher, he can increase the crown height of the diamond and therefore increase the weight without the diamond appearing larger. This will usually have a negative effect on the overall cut grade of the diamond and ultimately affect the diamonds light return.
The diamond’s plot is a map of where the inclusions are in the diamond. This map is like a fingerprint is to a person. There are no two plots which will be identical and is therefore an ideal way to match a diamond to a certificate. Sometimes the GIA certificate number will be laser inscribed on the girdle of the diamond for easier verification, however the plot is the best way.
The plot will have internal characteristics plotted in red and surface characteristics plotted in green. The plot will also have a key to symbols identifying what type of characteristic is placed on the plot.