501 4th Street, Sioux City, Iowa 51101

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Diamond Education

We’ve said for years, when you don’t know diamonds, make sure your jeweler does…and since 1900, diamonds have been our specialty at Thorpe’s. We are happy to take time to teach you about diamonds, or simply show you diamonds.

For those of you who would like a few basics first, we suggest you read about the 4 Cs of Carat weight, Clarity, Color, and Cut. It’s a helpful overview on how diamonds are graded and evaluated.

Others of you may be interested in the story of diamonds, and it’s to you that we suggest a click on our video, “The Diamond Dream” which will show the very human side and our global connection in the diamond industry.

THE 4 Cs – Carat Weight, Clarity, Color and Cut


Carat Weight

Measuring diamonds by carat weight began in the 1870s when diamonds were discovered in Kimberley, South Africa. Needing a basis of measurement so they could evaluate and sell the diamonds they were finding, the prospectors found a most unlikely standard in the seeds of the Carob trees that grow in Kimberley. The carob seeds, you see, are remarkably uniform in weight. Put on a scale, they could now measure the “carob” weight of the diamonds. A standard was born!

Though most people think of carats as an indicator of size, carats are actually a measure of a diamond’s weight. Diamonds are weighed in points. A one carat diamond is 100 points, a half carat is 50 points, and so on. The more points, of course, the larger the diamond. That’s where the size comes in.

But while we know “size matters” it is not the most important factor in computing the cost of a diamond…and as for quality? This is another one of those times that bigger is NOT necessarily better. Read on to learn more about the influence of the other Cs on diamond quality and pricing.


When jewelers like us grade a diamond’s clarity, we are evaluating its internal and external characteristics under 10X magnification. We are looking for the abnormalities that will affect the diamond’s value. Simply put: the fewer and the smaller the inclusions or blemishes, the better the diamond.

Inclusions are internal flaws inside the diamond, the most common ones being crystals (minerals trapped in the diamond) and feathers (fissures inside the diamond). Blemishes are external flaws that appear on the surface of a diamond and are usually very small.

As AGS jewelers that have been around a long time, we are especially strict in our grading of a diamond’s clarity. Among the industry we have noted a relaxing of the standards over the years, not unlike the “grade inflation” you may have heard about in our schools. Please know that what we called an SI-1 in 1965 is still an SI-1 to us, and not a VS-1 in our eyes. We see what we see and grade it accordingly.

You’ve probably heard the term “flawless diamond” before, used in the context of perfection, rarity, and expense. In this case it is the clarity of the diamond being held up to this lofty status. But an internally flawless diamond that is of poor cut or color is not a perfect diamond and may not be the wisest choice when you’re purchasing. Read on to learn how these last two Cs affect the diamond’s value.


This is the C that is most visible and easily discerned with the naked eye. While the jewelry industry uses a couple of different color grading scales, they all rate from colorless (most desirable) through nearly colorless, and increasing shades of faint to light yellow or brown (the darker being least desirable). True colorless diamonds are extremely rare.

To confuse the issue, there are also naturally colored diamonds, referred to as “fancy” which describes all colors other than colorless, light yellow or brown. The Hope diamond, which is a natural blue diamond, is the most famous example of this.

While increasing shades of yellow can reduce the price of a diamond, it doesn’t necessarily reduce its beauty along with it. As you read on about cut, consider that a well cut diamond’s refraction of light can make up for a certain amount of color carried in the diamond.


Diamonds have the unique ability to manipulate light, and this unique ability can only be released and maximized by cutting and polishing with an extremely high level of accuracy. It is a time-consuming effort, requires adherence to very strict geometric standards, but reaps the greatest rewards. Of all the Cs, cut has the greatest effect on the diamond’s beauty.

When AGS jewelers like ourselves are grading the cut of the diamond, we are evaluating the cutter’s skill in the fashioning of the diamond. We consider not only the proportions of the diamond, but also its overall symmetry and polish. We know that a poorly cut diamond may “leak” light and show less sparkle. A larger 1 carat diamond that is poorly cut and bottom heavy can actually appear smaller than an ideally cut 80 point diamond with more sparkle. Remember when we said, “Bigger is NOT always better?” This is one of those times.

This is also where we issue our final “Buyer Beware” message, for this is where you, the consumer, are most vulnerable. Lacking the training and the critical eye to discern the differences in diamonds, you can be prey for those that don’t have American Gem Society standards to uphold. Look, WE don’t buy diamonds online, WE don’t believe anybody’s Certificate or accept their grade until WE SEE the diamond for ourselves.

As always, we are happy to show you the differences at Thorpe’s so that you are able to make the best purchase possible. We will give you choices and options, but NEVER a poorly cut stone.

Conflict Diamonds

There is one more C of great importance to us, and we want you to know where we stand on this issue – and all the actions we have taken over the years, both to battle this and to ensure that our diamonds are conflict-free.

The term “conflict diamonds” was coined in the 1990s and refers to the sale of diamonds to finance violent rebel activities that occurred in parts of west and central Africa at that time. When word of this began to surface, the diamond industry as a whole acted swiftly and surely. While this illicit trade was a small, small amount of world diamond production, the overwhelming feeling was that even one diamond that was funding such regimes was one too many.

A program called “The Kimberley Process” was put into place and immediately supported by the United Nations and governments across the globe. It put into play a process whereby the source of a diamond could be documented and certified at every step to ensure that the trade in “blood diamonds” could be squelched.

At Thorpe and Company, we have always had a zero tolerance policy regarding illicit conflict diamonds. Even prior to the first awareness of conflict diamonds, our major source for loose diamonds had been Southern African Diamonds, which has always been a conflict-free production zone. You can be assured that any diamond purchased from us is certifiably untainted.