Cut & Clarity

I had originally intended to make separate lessons for cut and clarity, but these two topics are so interrelated it makes more sense to combine them into one lesson. The relationship between the size and price of a diamond is generally an exponential rather than linear relationship. By this I mean that as you double the size of a diamond, you quadruple the price of that diamond all other factors being equal. These prices are fictitious, but purely for example, if a 1 carat HVS1 diamond is $4,500, a 2 carat HVS1 diamond is $18,000 and a 4 carat HVS1 diamond is $72,000. The reason for this relationship is that a rough diamond that yields a finished 2 carat diamond is 4 times less likely to be found than a rough diamond that yields a 1 carat diamond.

But this is a gross oversimplification. Most regularly formed crystals from which round diamonds are cut are octahedral shaped. Typically, these raw crystals weigh roughly 3 times more than the finished product. It is a diamond cutter's job to maximize the selling price of every diamond that he cuts. Purely as an example, a diamond cutter might have a choice of cutting a 3-carat rough diamond into a well cut .90 carat diamond or a less well cut 1 carat diamond. This decision is further complicated by the fact that a diamond cutter can cut out imperfections entirely, diminish them, or move them to a less objectionable location. Again, these decisions are purely financial decisions that a cutter makes to maximize the value of the finished product.

But how does a diamond cutter know the likely selling price of his diamond? There are wholesale price guides that I have alluded to in an earlier lesson that are widely used in the trade to let a jeweler know what to pay for a diamond. These are the same price guides that allow a cutter to maximize his investment.

Here is where the interplay between cut and carats comes in. This is complicated so prepare a glass of wine for when this is over. Obviously, diamonds don't generate light so if you look at them in the dark, they don't work like a flashlight. Diamonds also don't really reflect light. Diamonds refract or redirect light (remember that 8th grade physics book?). The amount of light that is refracted back at the eye and not leaked out at an undesirable angle such as through the bottom (called the pavilion) of the diamond is determined by the depth expressed as a percentage of the diameter. The table size, the crown angles, the pavilion angles, and the girdle thickness. The white light that is refracted back at your eye (mostly through the table of the diamond) is called brilliance. The prism or rainbow colors that come back to your eye predominantly through the crown (the angled facets on the top

half of the diamond) of the diamond are called dispersion. A smaller table and bigger crown area would yield more dispersion and less brilliance.

Ideal cut, Hearts and arrows cut and GIA excellent cut:

This next section ending in 1-11 should be totally skipped by anyone who isn't OCD. It is designed to explain the ranges in attributes of diamonds with GIA excellent cut certificates. Around the beginning of the great depression a few years after my grandfather opened his first jewelry store, a Belgian engineer named Marcel Tolkowsky figured out that the ideal cut diamond would have a 34.5 degree crown angle, 40.75 degree pavilion angle, and a 59.3 % total depth. This information accompanied by $5 might buy you a cup of coffee today. Marcel Tolkowsy's cousin, Lazare Kaplan later refined these measurements to

• Table percentage: 53–57.4%
• Depth percentage: 59–63%
• Pavilion angle: 40.6–41°
• Crown angle: 33.7–35.8°

So, these measurements are the basis for what I would call an ideal cut diamond, and if it so happens that a cutter has cut an ideal cut diamond with such precision and symmetry that the diamond shows a complete pattern of eight arrows when viewed from the top and a complete pattern of eight hearts when viewed from the bottom, the cutter will have achieved a diamond which is not just ideal, but super ideal. The hearts and arrows are best seen with a special handheld hearts and arrows scope.

The GIA's criteria for an excellent cut grade are far looser, and revolve around the interplay of these factors:

1) Table 52-62 % of diameter

2) Depth 57.5-63% of diameter

3) Crown angle 31.5-36.5 degrees

4) Pavilion angle 40.6-41.8 degrees

5) Star facet length 45-65%

6) Lower half facet length 70-85%

7) Girdle thickness 2.5-4.5 %

8) Crown height 12-17%

9) Polish excellent- facet smoothness

10) Symmetry excellent- straightness and alignment i.e. intersection of facets

11) Culet none, small, or very small - the culet is the teeny facet at the bottom point of the diamond. The purpose of the culet is to prevent a jeweler from chipping this exposed brittle tip of the diamond when making a ring.

These ranges are extreme, but the GIA cut grade of excellent is determined by the mix of these factors.

Now back to the important stuff. I already mentioned the exponential relationship of diamond size and price but that, too, is a simplification. If you examine the price chart which is image 1 above, you can see that there are cut offs at

.90-.99 carats

1.00-1.49 carats

1.50-1.99 carats

2.00-2.99 carats

3-3.99 carats

4-4.99 carats

5 + carats

There was a wonderful old radio broadcaster named Paul Harvey that used to do 3- or 4-minute segments with a compelling intro to a story followed by a commercial after which he would reveal a bombshell ending which he would call " the rest of the story". Here is the rest of the story on size versus price. If there were a ton of 1.49 carat diamonds available on the market that were significantly less expensive than 1.5 carats, everyone would buy them. Unfortunately, a 1.49 carat diamond usually results from a miscalculation by a cutter. But, regardless, the size/ price relationship of a diamond is a geometric relationship even within a price bracket. The crude hand sketch above labeled 6156 is merely to show the exponential rather than linear size to price ratio even WITHIN a price bracket in exhibit 1. So, going back to the original example, if a 1 carat HVS1 diamond is $4500, a 1.3 carat HVS1 diamond might be something like $6500. The 30% size jump caused a 44% price jump.

Once you have an understanding of the price chart in the first image above, you are ready to understand the most important message of this chapter. I personally like to price diamonds by mm in diameter rather than carats. Since the price of a .95 carat 6.2 mm diameter diamond is so much less than a 1 carat on the price chart above, I want every 1 carat diamond I buy to be a 6.4-6.5 mm in diameter rather than 6.2 mm, and not look like a .90 carat. Why pay a 1 carat price for a diamond that has a thicker girdle or deeper depth and looks just like a .90 carat that costs $1500 less? In fact, I feel like the best value on a 1 carat round is a 6.6 mm that weighs more than 1 carat, a 7.5 mm that weighs more than 1.50 carats and an 8.2 mm that weighs more like 2.15 carats. I try to buy "plus" mm diameter diamonds in any given size bracket even if it requires paying a bit more for the extra carats.

So now you are almost ready for my answer to the customer who tells me they found a lower priced diamond online from someplace that sounds like Blue Smile. Do you think that the cheapest 1 carat HVS1 round diamond that you find on Blue Smile is identical to the most expensive 1 carat HVS1 diamond that you find on Blue Smile? The prices of the 1 carat HVS1's might vary by 100%. Why would anyone buy the more expensive one? The answer is the cheap one has strong blue fluorescence (next lesson), a 6.2 mm diameter, a brown tint not disclosed on the certificate, and/or a small black speck in the table. And, by the way, Blue Smile doesn't own the diamond, and it is currently located in India so you will have to pay for it in full in order to see it. Don't let me forget to offer you "good luck" while you are waiting for your refund if you don't like it.

One last thing. When you find the diamond with the color and clarity that you like and it is not triple x, meaning excellent polish, excellent symmetry, and excellent cut, should you buy it anyway? For your information, a diamond that is not triple x absolutely could NOT be recut to triple x and maintain the weight category that it currently falls into on the price chart at the top of the page. Otherwise, the diamond cutter would have already done it. So what??? If it is significantly cheaper than a triple X AND YOU LIKE THE WAY IT LOOKS, and it has a good spread (mm diameter), then you have my blessing to buy it. But read the next paragraph first.

What about diamonds that are not mostly excellent or very good polish, symmetry, and cut? These should be purchased based on what it would take to recut them to very good or excellent cut. The weight loss as a % of total weight, the fact that the smaller diamond will then fall into a smaller size bracket on the chart above, the recut cost of $100-200 per carat, the recertification cost of $100 per carat, and the round-trip postage and insurance to the cutter and lab must all be considered. In most cases, I personally would not buy a diamond that is only good or fair cut, polish or symmetry unless the price is a minimum of 50% or less than that of the comparable triple excellent stone.