Gemstone Cutting Flaws

Most gemstones on the market are either cut by machine or cut on rudimentary machines. As a result there are a lot of gemstones out there that have a lot of issues and in my opinion, are less beautiful.

I had mentioned in this post, Considering Gemstone Recuts, about recutting two stones for repair, and one for appearance sake. I would like to go a bit more in depth as to what these cut flaws can look like, and why they are considered flaws.

Please note that I am not a lapidary and do not have as stringent guidelines as they might for what makes a beautiful gem.

Windows

Windowing in gemstones is when the gemstone has what looks like a hole in the middle and the stone is completely see through without sparkle in the middle. What is happening here is that the facets on the pavilion of a stone is cut to such an extreme angle, so that the light goes into the gemstone, and straight back out the bottom. These facet angles on the pavilion can run almost parallel to the table of the gemstone. Here is a good example of a windowed gemstone:

Pad6

Windowing can occur two different ways, the first being when the gemstone is cut too shallow, typically to preserve a larger face up size for the stone. This cut flaw cannot typically be corrected without significant loss to the faceup size of the gem. This can also affect the value of the gemstone in a big way, losing valuable carat weight and face-up size.

The second occurs when a stone is cut at the wrong angles for the gem variety. The stone typically has a “fat belly” or “fat pavilion” or looks rounded on the bottom, more like a ball than coming to a sharp point, or culet, the way you would expect a gemstone to be cut. These stones are typically cut for weight retention. Here is the stone from my previous post that has this flaw, a silver spinel:

pavilion1

pavilion2

A deep belly/pavilion can typically be corrected with some tweaking by a talented gem cutter.

Tilt Windows

Tilt windows can be seen in every single gemstone variety, including diamond, but are most often seen in stones that have a lower refractive index, such as tourmaline, topaz, quartz and beryl. Tilt windows can be seen when a stone is being viewed from an angle that isn’t straight on. Stones with lower refractive index will show windows more easily. Please note that all of the stones seen in the following examples are cut by talented precision lapidaries.

Tourmaline tilt window:

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Slight tilt window seen on the left side of the garnet in this picture:

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Slight tilt window in a asscher spinel:

IMG_5373

Extinction

Gemstones can be cut to incorrect angles to the point where they black out, or when light goes in, but does not get reflected back to the eye. This type of problem is called extinction, and is a serious flaw because if a stone looks black instead of being a nice color, what’s the point? Some gem cutters expressly cut stones so that facets take turns turning off and on, this effect would be considered being cut for contrast, rather than plain extinction.

The dark blue spinel on the bottom is showing a bit of extinction, while the stones above it (sapphire and spinel, respectively) are not.

gem photobomb17

Half and Half Shadowing

Half and half is typically another result of less than ideal cutting, and is also a mechanism of physics. It’s a specific type of extinction, so it is a result of light going into a stone and not being reflected back to the viewer’s eye. However, this particular type of extinction is typically seen in an elongated brilliant cut stone such as cushions, radiants and ovals. When these stones are viewed North-South, the phenomenon is very visible, but when the stone is viewed East-West, it can become essentially non-existent.

The dark blue spinel (same from above) on top shows it’s dark side on the upper half.

gem photobomb7

A purple sapphire shows some half and half darkening on the top half of this stone.

purple sapphire5

This stone is a spinel, and you can clearly see the half and half as well as a bit of a tilt window.

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So, while none of the above are deal breakers when I look at a stone, they are still qualities to take into consideration when purchasing gemstones and looking for beautiful jewelry. Any gemstone variety can have the above cut issues, they are not limited to any one particular gem over another. One way to mostly bypass these issues is by finding a lapidary and checking out their inventory, but that is not a guarantee!

Spinels: Scale of Gray

I started this blog talking about gray gemstones. When I started my search, I kept coming up empty with what I wanted, until a gemstone that was pretty under appreciated came to my attention – gray spinel. But there wasn’t really any out there.

It turns out that people are reluctant to cut a gray gemstone, because everyone wants bright highly saturated gemstones.

These are some of the stones that were bought (and some since sold) in my quest for exactly what I wanted. One note about gray spinels is that they are incredibly difficult to photograph. They are very temperamental and reflect everything in their environment, and as a result, they are exceptionally problematic to photograph.

The Scale of Gray (SOG) is a scale of 1-10, with one being colorless and 10 being black. The idea for this was based on the art and graphic design principle of grayscale: Wiki article on Grayscale

grayscale (1)
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Image taken from google image search)

These two spinels are almost colorless. Spinel is typically not colorless and almost always has a modifier of some other color. To be colorless, spinel cannot have impurities. These spinels are so close to colorless that I cannot discern a modifier in them. I consider these stones a 1 on my Scale of Gray. The round stone looks darker here than it is in real life. I will attempt to get a better picture of it and replace it at some point in time.

Round stone: Artistic Colored Stones
Pear Recut: Gemart Services
1
Grey 1b

This spinel is a very slightly silvery gray, so much so that it’s almost imperceptible unless the stone is on a white background. It can appear colorless at times, especially when in a bright lighting situation. I consider it a 2 on the SOG.
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This stone is deep enough in tone so that the gray color is apparent even when the stone is on a colored background, such as skin, as seen in this picture. This stone can appear to look colorless in certain lighting conditions. I consider this stone a 3 on the SOG. Round: Jeffery Davies Gems & Jewelry
Grey 3

This stone is what I consider a 4 on the SOG. It is definitely gray in most lighting situations and never appears colorless. Sometimes it can look lighter gray and sometimes it can appear a darker gray, but only blacks out under bright direct sunlight. Round: Julia B Jewelry
Grey 4 (2)

I consider the following stone a 5 on the SOG. Sometimes it appears to be a lighter gray, and sometimes it appears to be darker, but the body color is a clear medium gray. Round stone: Artistic Colored Stones
Grey 5

This asscher cut from Ryan Quantz is finally being added to the the line up as a 6.  This stone always appears gray, sometimes can appear silvery when the pavilion facets reflect light, and sometimes can appear black in very low lighting situations.
6b

This stone is what I would consider a 7 on the SOG. It often appears darker gray and never appears colorless. Sometimes the facets reflect light, making it appear medium gray, but overall, this gray color is always going to appear to be darker.
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This spinel is an 8. It’s body color is decidedly dark, and unless it is in very bright lighting situations, it will appear to be very dark or black.
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I consider this stone to be an 8.5 on the SOG. It is a darker gray, often appearing to be black, and when it does not appear black, looks very dark gray, and may have a lighter flash move across the pavilion facets. Cushion: Gemcal
8-5

I consider this stone a 9 on the SOG. The majority of the time, it appears to be black, and only sometimes appears to be gray, typically with sparks of color. Black is considered the absence of light, so I cannot in good faith call this “black” because light travels through it to some extent. Cushion: Custom Gemstones
Grey 9

I feel as though there has been an increase in popularity in gray spinels, which is great and terrible, all at the same time. I think it’s wonderful that people are giving attention to a neglected color, but at the same time, they are driving up demand, and as a result, prices.

I am constantly on the lookout for these underappreciated gemstones. Nothing really makes me quite as happy as an amazing gray spinel!

Gem Blast: Considering Gemstone Recuts

I typically like to do Gem Blast posts as mostly pictures with little commentary, as it gives me a little break from writing, and I get to post pictures, which I love taking, but this one is a little bit different because it deals with a specific issue: Gemstone Recuts

This stone started out coming to me from ebay, and is a hot pink spinel from the Mahenge area of the Morogoro region of Tanzania. It was 1.8cts, and 7x6mm. It wasn’t until owning this stone for well over a year that I realized that it had a horrible crack in the pavilion, along the keel. I enlisted the help of  Jerry Newman of Gemart Services to see if it could be cut out and let me tell you, that man is a miracle worker.

Hot pink5 (2) hot pink3 (2)

 

Amazing color! But if you look carefully at the above left image, you can see something funky going on on the keel from the face down view. But when you flip it over and look at the keel through a macro lens, it makes sense.

crack4 crack2

crack3

 

So I sent my stone to Jerry. He had said that he thought he could get rid of that nastiness without it affecting the face up size. Once he was done, and he is very very fast – I got the “It’s done!” email less than a week after he got it – he said that he thought he could recut it again and make it more brilliant, but he wanted to know my opinion. After the recut:

 

MorePink Hot pink5

 

Obviously I liked the stone just as it is, and didn’t want to lose more material or risk the loss of more saturation. It is difficult to tell because the environmental situations are different from the “before” pictures, but the stone lost a little bit of saturation. However, Jerry managed to only recut the pavilion with no loss to the face up size. It went from 1.8cts to 1.55cts, and actually became more stable since the liability of the crack on the bottom was eliminated. The clarity was improved as well since the fuzziness that the crack created went away.

Hot pink1 Cushion

Because of the overwhelming success of the above pink spinel, I have started considering recutting a few other stones of mine…

Silvery spinel, 5×7, considering a recut on it to improve performance. It currently has a small window, and a bowtie. Sometimes it even shows a bit of half and half shadowing. I think it’d be gorgeous if it had some improved cutting. It has a bulgy pavilion, so recutting it should be relatively simple and improve it significantly. I actually think the stone is nice to begin with, with a really cool light gray, but I think the risk is small enough and the payoff good enough that I think it should probably be done.

2 3

4 5

Possible Emerald Tourmaline recut. This is a different case because this stone started out as a precision cut stone from Master Cut Gems. It has a gorgeous color, but it was very badly chipped (mangled?) when it was set in a setting. Unfortunately I didn’t realize this until long after purchasing the original ring. Luckily I had a stone that would fit into the setting, so it wasn’t a total loss, but the stone is pretty much unable to be reset because it’s so badly damaged. Here is a picture of the stone from Dana at Master Cut Gems before it was set:

tourmaline emerald

Beautiful color, eh? It’s a great teal, not too dark. And here is the stone after being unset, under my macro lens, which makes everything look dark and shadowy, since it is black:

 

Teal

 

You can see in this image how smoothed out the chipping is, with no sharp edges, showing that it was done quite some time ago, and is not new damage:

Teal2

 

I have a macro picture of the stone in the setting, and you can just barely make out the mess under the one set of double prongs. This is the mess on the opposite end:

Teal3

Another view, giving an idea of the slight bicolor (green on one end, blue-green on the other) action going on with this stone, as well as showing the wear on the facet junction on the meet between the crown and the table facets.

 

Teal5

 

So, I’m kind of playing with the idea of seeing if it would be possible to cut all of the bad stuff away, and leave something that could be used. I have talked a little bit before about my love of all things step cut, so it really pains me to chop this up, but I think there might be potential to cut another step cut out of it, perhaps a shorter emerald, a carre or an asscher. Unfortunately, this stone is a smaller 1.07ct (the chip is probably big enough to decrease that!) so it’d probably end up being about 5×5 and maybe .60ct, so I don’t know that it’d make a lot of sense to do it, but I might do it anyway because it’s such a great color.

Teal6

Gemstone recutting, or cutting of rough is not a job to be taken lightly. It takes an immense amount of talent, intestinal fortitude, luck and knowledge to produce these small sparkly items. I have nothing but the utmost respect for lapidaries because it is not an easy job, and clients can be hypercritical of the results. I greatly admire those that do it, especially recutting damaged stones and cutting from customer’s rough because of all of the risk involved. Every time I have gone into a jewelry project with something I’m unsure about, I have a pit in my stomach until it is completed, and when the risk is the total ruining of a gemstone, the risk is really quite high, and not something to be attempted on a whim.