Tag Archives: gem grading

Gemstone Cut Grading; Distinctions Without a Difference II

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by Richard W. Wise, G.G.

©2012 all rights reserved.

Of Tilt-Windows, Off-center culets and other minor issues:

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The image of the gem quality 1.44 carat alexandrite might lead the uncritical observer to conclude that the gem is windowed. What the gem is actually exhibiting is some extinction beneath the table. In a perfect world, both are minor faults, but we are talking about the rarest gem on earth. In the world of true rarity, beauty not mathematical perfection of symmetry is the ultimate criterion.

The first time I ever heard  the term tilt-window was on the Pricescope forum.  As you know, a window is a part of the gem when viewed face-up that exhibits transmitted light.  Windows are almost always found right beneath the table.  A quick test is to place the stone over a piece of newsprint.  If you can read the print, you are looking through a window.  Windows are the result of a shallow pavilion, a too shallow depth to width ratio.  Windows are considered faults because they are a portion of the gem that does not sparkle.

Gem cuts are designed and engineered to be judged face-up with light perpendicular to the table.  Tilt the gem away from the perpendicular and every gem other than a briolette will exhibit a window. Ironically the more precise the cut, the more likely the gem is to window when tilted as little as five degrees from the perpendicular.  Some gems, particularly those with a bit of fat around the pavilion, may exhibit some brilliance when tilted as much as ten to fifteen degrees from the perpendicular.   What cannot be eliminated must be embraced.   A tilt window, forgetaboutit!

Grading; From Minus To Plus:

Gems with bulbous pavilions are often criticized for being overweight, meaning that the stone’s face is smaller than it would be if the stone was perfectly cut.  The irony here is that such stones may actually exhibit a greater arc of brilliance which contributes to the beauty of the gem.  Once the eye is four to five feet from the gem, the overall brilliance becomes the real issue, not the stone’s mathematical diameter.    Broader bellies also extend to the length of the light path and may enrich the  color (hue, saturation and tone) of the gem.

In another Pricescope thread, one ubiquitous poster put a link to an alexandrite (pictured above) on my website and criticized me for the failure to disclose an off-center culet.  How did this forum member determine that the stone had such a terrible fault?  The page included a side view image of the stone face-down.  If there was an attempt to hide the fault, it was hidden in plain sight.  http://www.rwwise.com/products/id,255   Unfortunately her interpretation of the image was quite wrong.  The stone does not have an off-center culet.  What the forum member saw was a very minor symmetry fault, one side of the pavilion has a slight indent coupled with a tilted crown which when placed on a flat surface caused the culet to appear off-center.  And if the gem did have a slightly off-center culet, so what!  We are talking about one of the earth’s rarest treasures, a gem quality alexandrite!

Each Gem Is an Individual with a distinct personality and should be judged on its merits:

Gem aficionados usually begin their love affair with the colorless diamond.  They learn the famous 4 C’s and attempt to apply those criteria, namely color, clarity cut and carat weight uncritically to colored gemstones.  As I have said elsewhere all Cs are not created equal.  In the connoisseurship of colorless diamond, cut is the 1st and most important criterion.  Diamonds have no color, they are all about  brilliance and sparkle, so naturally cut, which delivers sparkle is the most important single criterion.  I knew a neophyte jeweler once who was not satisfied with eye-flawless sapphires, he demanded that all of his sapphires be flawless under 10x magnification.  The problem, without inclusions it is almost impossible to determine if a stone has been enhanced and determination of geographic origin is absolutely impossible.

Colored gemstones as their name suggest are all about color and cut is, at best, a secondary consideration.   An off-center culet in a diamond would be a major symmetry fault and materially effect price.  In a colored gem, an off-center culet in and of itself is a minor fault which has no effect on price.  Why do such things exist?  A culet might appear off-center for a couple of reasons.  The lapidary may have removed a potentially eye visible inclusion or have placed the culet slightly askew to smooth out color zones so that the zone does not appear in the gem when viewed face-up.

It should be remembered that colorless diamonds are not truly rare.  The introduction of cut and clarity scales that have nothing to do with beauty are more about creating the appearance of rarity than the thing itself.  The connoisseurship of gemstones requires discernment and careful contemplation.  Gems cannot be accurately graded by image.  The aficionado should beware attempts to reduce it to a formula or a check list.

Evaluating Gem-e-Wizard; Gem Grading/Pricing Software

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©2011 by Richard W. Wise, G.G.

First off, Gem-e-Price is the first grading/pricing software that I have evaluated and working with it was a lot of fun.  With the recent addition of colored diamonds, Gem-e-Price is now able to offer a price structure for just about all species and varieties of colored gemstones.

Gem-e-price offers three ways to approach the evaluation/pricing process.  I say evaluation because, although gem-e-price is sold as pricing software, the ability to select quality is a necessary precondition for determining price.

Ease of Use:

The software is easy to use.  First you are presented with a fairly clean screen with buttons and drop boxes.  There are three tabs;  Fancy Search, Price List and Price Calculator.  The default screen, Fancy Search allows you to select a gem variety, size, shape, weight, clarity, treatment.

Gem-e-price Home screen

Gem-e-price Home screen showing range of colors in yellow diamond.

Unfortunately it didn’t take long for the first bug to appear.  Once you select “color” (primary hue) and “modifier” (secondary hue) and move on to shape, you quickly realize that though you can select your shape from a graphic series, only two shapes will actually appear in the gallery, select round or square cushion, choose any other shape and square cushion is shown.

The images, which in the colored diamonds section covers the basic grades, fancy through fancy dark,  are not pictures of actual gemstones or photographic images at all, they are graphic representations.  When I first saw these during the introduction of gem-e-price for colored gems, I referred to them as grading by cartoon.  However, one function of the software helps overcome this lack of veracity to some degree.  Once the color has been selected, say yellow, the “Fancy Ruler” button to the right will take you to a screen with a spectrum representing all colors, from there a “Select Color” button in the center of the screen takes you to a new screen with all permutations of the given color (hue): brownish yellow, brown yellow, orangy yellow and so forth.   You get a good relative overview of what the graphic range is supposed to represent and is useful for honing in on the appropriate nuance of color.

Gem-e-price screen showing range of primary and secondary hues in pink diamonds.

Gem-e-price screen showing range of primary and secondary hues in pink diamonds.

It also provides you with a more or less universally accepted color descriptive  shorthand, e.g. VpB (vivid purplish blue).  I should add that you are able to upload, at the home screen, an actual image of the diamond that you wish to compare and that image follows you from screen to screen.

Nomenclature Issues:

Is the pricing accurate?  As Shakespeare said, “aye, there’s the rub.”   The answer is yes, no and sometimes.  I compared the Gem-e-price with a couple of my own diamonds, then called colored diamond expert Stephen Hofer author of Collecting and Classifying Coloured Diamonds and compared various price lists, pink, gray and blue diamonds generated by the Gem-e-price software.  The prices made no sense at all until in a conversation with Gem-e-price developer, Menahem Svedermich, he revealed that the price is pegged fairly low.  This will require a bit of explanation.

The point I make in my book, Secrets Of the Gem Trade, is that all fancy vivid diamonds are not created equal.  GIA’s colorless diamond grading system has 24 grades, the GIA colored diamond grading terminology has only between 5-7 depending upon the hue.  These are fancy light, fancy, fancy intense, fancy vivid, fancy deep and fancy dark. In the vivid category, for example there can be high, medium and low vivids depending upon the saturation/tone of the hue.   Gem-e-price assumes a 1-5 saturation grid at each level and pegs its price to level 2.  Why not the median?  Good question!  Well, one week later, Gem-e-price has been updated, it now sports three price levels for each color grade, Regular, Fine and Extra-fine categories and these have helped to better define price levels.

Pricing Accuracy:

With Hofer’s help I took a look at a one carat Fany Intense Pink  diamond( FIP).  A two thousand dollar spread, in pink diamonds, hardly worth mentioning, the price was spot on.  I then went to a 0.70  FVY-O from my own inventory.  This is a problem stone, The GIA grading report calls it Y-O, to me its a orangy yellow (oY).  So, I tried it both ways.  The Yellow-Orange price was way out of the box, the Orangy-Yellow was pretty close to my actual cost.  Next I tried a 1.75 Fancy Intense Blue IF which Hofer described as a top stone.  The Gem-e-price was between under Hofer’s price by between 100-200,000 per carat—sounds like a lot but we are talking blue diamonds here so it is fair to say that Gem-e-price is in the ballpark.  I did some further work, switching over to colored gemstones I priced out emerald, ruby and sapphire.  The emerald and sapphire prices came out in the zone, the ruby price, we are talking super-unheated-gem in one carat sizes came out very high.  I asked Antoinette Matlins author of the second best book on colored gemstones—opps there goes my Bonanno award—she checked my price and reported results that were similar to mine.

Overall Evaluation:

Overall I like it.  Is it perfect, no!  It is designed for professionals, in the hands of someone without a wealth of experience it could be a potential disaster, but then what isn’t?  Gem-e-price is a useful tool, its got a few bugs, but it is getting better, Svedermich and his team made adjustments as I worked and will, I am sure, continue to improve the product.  I like the price grids!  A subscription with monthly updates is $300.00 per year and, in my opinion, well worth the price.