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How to Judge the Quality of Diamonds

What to Look For

To begin judging the quality of diamonds you have to have an undrestanding of the 4 C's. These are cut, clarity, color and carats. Each one of these has an effect on the cost of the diamond and fine diamonds will do will in all four areas. If three are excellent and the forth is poor then the value of the stone plummets. The diamond shape doesn't necessarily add to the value of the diamond, but does help to add some variety.

Judging Color

Most diamonds are considered to be ideal if they are transparent, or colorless.  Diamonds that are rated as colorless are the most expensive of diamonds that are readily available.  (Fancy naturally occuring blue diamonds, or other colors, are rather rare and difficult to find. Treated diamonds are more common.)

The colors of diamonds are rated with an alphabet grading system that starts with “D” and ends with “Z”.  Completely colorless diamonds fall in the “D” and “E” grade, while colored, fancy diamonds are at the other end of the alphabet, at “Y” and “Z”. 

There are two main ways that jewelers’ use when judging diamond quality based on color.  They may pull out a set of reference stones, and find the closest match between the diamond and the reference stone to determine its letter grade.  Alternatively, the jeweler may use a colorimeter, which can electronically measure the color of the stone and determine its grade within 1/3 of a grade. 

Judging Clarity

The clarity of a diamond refers to whether or not the diamond is clear all the way through, or whether it has tiny flaws and cloudy areas within the gemstone.  It’s actually very rare to have a diamond with absolute perfect clarity and no flaws, but most diamond flaws are not visible to the naked eye. These flaws can only be seen with a magnifying device and only properly interpreted with suitable training.

The Gemological Institute of America (GIA) uses a magnification of about 10x when judging diamond quality based on the clarity.  There are treatments available to make a diamond appear nicer than it actually is, and the treatments should lower the overall price of the diamond so it is important to do your research before purchasing a diamond to be sure you are not spending more money than you should. 

Judging Carat Weight

Carat is the term we used to describe the weight of a diamond gemstone and it's a lessor factor in the cost of a diamond..  One carat is equivalent to 200 milligrams of weight.  so 10 carats = 1 gram. A 10,000 carat diamond wouild be 1 kilogram in weight. The biggest diamond ever found was, in rough condition, about 40 grams (400 carats.)  Head off into outer space though, and you might find something bigger...

A single diamond with a high amount of carat weight is more expensive than the equivalent amount of carats in multiple stones. This is because as the size of the stone increases so does the rarity. Very large diamonds tend to fall into the priceless category. 

So if you want a 2-carat diamond ring, for example, you may decide to go with a half-carat diamond surrounded by smaller diamonds that add up to one and a half carats to give you the total of 2 carats!  It won't have the value of a two carat stone, but your wallet won't cry as loudy. Judging diamond quality soley by the amount of carats is impossible, since different shaped gemstones, and stones with different levels of clarity, will be priced differently even if they have the same amount of carats.

The cut and clarity of the stone are more important in pricing than the size.

Judging Cut

One of the most important factors in judging diamond quality is judging the cut of a diamond.  It’s important because a quality cut diamond will be more brilliant and reflects light more beautifully. A nicely cut diamond will always be much more valuable than one that isn't so well cut, even if everything else is equal.

When judging diamond quality on the cut of a diamond, look at the stone in a well lit area.  If the light seems to go into the stone and bounce back, showing a sparkling reflective surface, the diamond has a good cut.  The angles and shapes of a diamond are important to judging diamond quality and the overall appearance of your diamond. Some few diamonds can be cut perfectly enough to display hearts and arrows. The perfection of the cuts required drives up the costs of the diamond by a considerable amount.

© 2006