Tanzanite Cut - Often Overlooked but Very Important 

GIA Gemologist Article Series on Tanzanite


Cutting is one of the "4 "C's" of value but is often overlooked. Cut can play a central role in Tanzanite value and fine cuts command up to a 30% premium over cuts done with weight maximization techniques. This article attempts to explain what to look for and how to understand cut.

One of the 4 C’s that is often overlooked is the quality of a Tanzanite’s cut. Cut goes beyond just the shape you may be looking to purchase and plays a large part in a Tanzanite’s value, ease of setting, beauty and grade. Due to the channel of distribution established by TanzaniteOne in the past few years, most Tanzanite is cut in India by companies called “sightholders”. The vast majority of Tanzanite passes through the cutting centers in India before going on to various world markets.

The principal objective of these cutting centers is to maximize weight retention as they get paid based on the finished carat weight. Hence it is in their interest to cut a stone as heavy as proportions will allow to maximize their return. This is of great benefit to the companies in the chain of distribution as they get a larger return on their rough investment but it is ultimately not to the advantage of the end buyer, who ends up paying for weight that is not required and can have a negative effect on beauty and quality. What’s more, it effectively adds between 15% and 30% to the real cost of the stone. A 10 carat stone for example would be 7 or 8 carats if cut properly. Cutting for weight retention leads to several problems:

• Windows
• Loss of brilliance
• Difficulty in setting
• Bad Symmetry

Let’s go through these problems one at a time

Windows

What exactly is a window? It is simply a “dead” area in the middle of a gemstone where there is no light reflection which has the appearance of a “hole” or “empty space”. This is caused by either cutting a stone too shallow or cutting it too heavy in the back or with too high a crown angle (the top of the stone). Many cuts done in India have both these problems due to weight maximization. Stones are cut shallow when a piece of rough is flat and a cutter wants to use as much of the face up size as possible, so cuts a wide stone with a very shallow back. Similarly, some stones are cut with bulges in their pavilions (backs) maximize weight retention. This is demonstrated below.

Bulged-Pavilion.gif

Similarly, some stones are cut with long keel lines to increase the volume of the back of the stone, rather than cutting to a point, as it should be. This is a well known weight saving technique. This is demonstrated below.

Keel-line.gif 

>To keep as much weight on a Tanzanite as possible, a cutter can use very high angles on the crown (top) as well as the pavilion (back) which can retain as much as 30% of carat weight against a stone cut properly. These picture below demonstrates this (please forgive the obviously Photoshopped image, Tanzanite doesn't look like this but we thought it interesting to show how some sites are representing colors) 

Crown-High.gif

What this means is that you go ahead and purchase a Tanzanite of a certain weight but end up paying for up to 30% you don’t get any benefit of and can actually cause problems in the setting and be detrimental to beauty and symmetry. This adds a fair amount to the real cost of the stone.

Loss of Brilliance and Difficulty in Setting

Tanzanites cut for weight generally sacrifice some beauty. Even if the color is beautiful, the stone can appear dead and lifeless. Difficulty in Setting - some stones cut for weight maximization can be more difficult to set due to thick girdles and bulky pavilions (backs). This can make it easier for a stone to be lost out of the setting. It also adds to the risk of breakage during setting.

Bad Symmetry

One of the characteristics of stones cut for weight is bad symmetry. Stones that are not straight or have unsymmetrical facets are not beautiful. Some examples below.

Symmetry.gif

Note how some of these are sitting at an angle – this is because the back is so skewed that they cannot lie straight on the flat surface. Others show obviously bad symmetry on the facets on the top. Of course the old bugbear of weight maximized stones, the window, is present in most.

So What is a Good Cut in Tanzanite?

There are several considerations when cutting gems. First, the angles that are used on the table (top) and the pavilion (back) must be carefully calibrated to be within what gemologists call “the critical angle”. To explain – as light passes into a gem it does so through the table (top), hits the back facets and bounces back through the table (top) to your eye. To achieve this, a stone must be cut within the critical angle of the mineral. To explain – all minerals have a different critical angle within which light will bounce back within the stone (called internal reflection). Stones cut outside this will show a window. This is demonstrated in the diagram below.

Internal-ReflectionA.gif


Stones cut for weight invariably have this problem. The video below shows several Tanzanites with proper proportions. The pavilions (backs) come nicely to a point, angles on the back are sharp and not bulged and facets are symmetrical.

 

 

So Putting it all Together

Cut is an important factor that can increase weight unnecessarily whilst impacting negatively on the beauty and value of the piece. It can add up to 30% to the real cost of the stone, sometimes more in really bad cases. Consider cuts carefully and if you are looking to buy the top grade, make sure the cut is optimal otherwise the piece cannot be considered top grade. A stone may look like a good deal because of the price but a bad cut can push your real cost up a lot. That is why top cutting commands a premium – more of the Tanzanite is lost from the rough during the cutting process. Cut quality is one of the important 4 C’s and it shouldn’t be overlooked


 

This series of GIA Gemologist written articles on Tanzanite is provided to create a greater understanding of Tanzanite value and quality in the face of increased misinformation on the internet today. Others in the series are listed below. Click on each to read them:

Tanzanite Color How it Affects Value
Tanzanite Cut Quality - Often Overlooked but Very Important
Tanzanite Color Grading Systems - Which to Trust?
Tanzanite Clarity - How it Impacts on the Grade
Tanzanite Trichroism - The Mood Changer
How to Care for Your Tanzanite

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