What is a Window in a Cut Gemstone?

window of a gemstone

A lot of us who love to wear a gemstone have little or no knowledge about gemology or lapidary basics. But that does not stop us from longing for these amazing natural beauties. Some us may have never even heard the term ‘window of a gemstone’ and why it is so crucial for the buying decision.

An unassuming buyer will very well may end up paying a huge sum for a precious stone for its visible color and carat weight not knowing the quality of the stone is seriously hampered by the windowing effect.

In this article we are very closely examining how to identify a gemstone window. Further we will look at why a window is created in the first place. If your ring already have a windowed gemstone, we discuss remedies for these as well.

How Do You Determine the Quality of a Gemstone?

Let’s start with the basics. A widely used measurement to judge the quality of a cut gemstone is 4 Cs rule. 4 Cs stand for color, clarity, cut and carat weight.

Color is usually the most sought after feature an amateur buyer is looking for. The color of course is the main aspect of a gemstone that decide the value. However color is not the only factor.

A well cut gemstone
A Good Cut

You need to also closely inspect the clarity. The more the inclusions, the less the value. Then the carat weight. All sapphire and gemstone sellers will emphasis more on the carat weight as it drives the total selling value.

Usually what comes last is the cut. But it will have a huge impact on the value if not done correctly. It could be a matter of paying a 1,000 vs. paying 1,500 dollars per carat. You are also missing out a good bargaining chip if you not know about the cut and possible windowing effect.

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What are the Factors Affecting the Cut of a Gemstone?

A natural gemstone is found in earth and produced through a mining process. A gemstone is not so difference from any other random rock you find in your back yard, except for the color and apparent luster. This is what we call a rough gemstone.

Ceylon Blue Sapphire Rough
A Rough Ceylon Blue Sapphire

As you can imagine, a rough gem can look like anything. The gem crystals form in different shapes and sizes with different dimensions. A rough that is found in a mine then needs to be cut to enhance the value properties. The gem cutter is one who decides how quality the final product will be.

Following are some aspects a gem cutter will look at.

  1. Retaining the carat weight
  2. Maintaining the color bands within the cut specially if the gemstone is doubly refractive
  3. Avoiding inclusions in the final cut
  4. Enhance the brilliance

Thus converting a rough to the cut gemstone requires a high level of judgmental skills along all these factors. Over doing or under performing on any of these aspects will hinder the price of a gemstone.

What is the Windowing Effect of a Gemstone

The windowing effect is more of a technical occurrence resulted by a bad cut. Each gemstone has its own hardness. While diamond scores a 10, sapphires and spinels score 9 and 8 respectively in Mohs hardness scale.

The light that hit on to the table of the gemstone perpendicular to the surface will directly go in. Based on the density of the gemstone, the light that enters will get refracted from the bottom facets. For each gem type, based on its hardness there is an angle called ‘critical angle’.

Window of a gemstone
Too Shallow, Good and Too Deep Cuts

When those light rays hit the bottom surface in equal or greater angle than the critical angle, the light gets completely refracted and turn back into the stone. A bad cut gemstone will have inaccurate facet angles that refract the light out of the bottom or sides of the pavilion of the gemstone. This will reduce the brilliance significantly. The top view looking down from the table will completely be transparent. This is what we call the windowing effect.

A bad cut gemstone with a window
A Window in a Gemstone
Window in a gemstone
A Bad Cut

This phenomena is absolutely critical for gem cutting. Each different cutting style has it’s own set of angles. A cutter who has prioritized saving the carat weight or maintaining the color band and avoiding the inclusion over creating brilliance will probably end up putting a window in a gemstone.

How to Identify a Window in a Bad Cut Gemstone

Identifying a window is absolutely necessary when you buy a gemstone. A prominent window can drastically hamper the value of a gem regardless it’s carat weight. There are couple of quick ways how you can spot a window.

1) A window as the word suggests works as a gateway for the light to pass through. If you put the gemstone on top of a printed news paper, you can see the small words beneath. This is a the key sign of a bad cut windowed gemstone.

See through gemstone
Bad Cut Gemstone with a Window

2) It will also appear significantly less brilliant under different lighting conditions. Do not let the seller to brighten up the stone from side facets. Once you set the stone on to a ring, there won’t be much light entering from the side facets. Your judgement should be completely on the light entering from the top.

Less brilliance
Less Brilliance

3) The crown facets will particularly look darker or sometimes completely black. This is because there is no light coming back out from the facets to your eyes. Some stones colors may anyway be darker depending on the shade and also the transparency. However if you see a light color table and darker crown facet, it could most likely be a bad cut.

Dark facets of a bad cut
Facets Appear Darker with a Light Center

4) If you have some experience in handling gemstones, you will see the cut is either too shallow or too deep for the side of the crown and table. Both shallow and deep cuts are considered bad cut gemstones that can exhibit a window. Make sure the ratio of the gemstone to its top view width and depth is not abnormal.

What are Remedies Available If My Gemstone Already has a Window?

Do not worry if you already have a bad cut windowed gemstone. You can always have it re-cut by an experienced cutter. But this is always not possible.

This depends on the intensity of the windowing effect and the current size of the gemstone. If the window is very prominent and the gem is quite small, say less than 1 carat, the chances are slim to correct it. You may end up exhausting the complete stone.

However there’s always a chance you can re-cut. A re-cut however will reduce the carat weight and size of the gemstone even up to 50% or even more depending on how bad the original cut is. A too shallow stone will require the cutter to reduce the table and crown size. A too deep cut gemstone, however can be rectified without reducing the table and crown size and also not affecting the carat weight too much.

Re-cut a windowed gemstone
A Window is Closed with a Re-cut

Therefore you must carry out a re-cut only after assessing the total benefits vs loss. Reduction of the carat weight, the improvement of the overall value and the cutting fees has to be at least balanced out. A well cut gemstone is valued more and look for fabulous than a gemstone with a window.

If you identify the window effect before you set it on to a ring or jewelry, you can also ask your jeweler to attach a small reflective aluminium paper beneath the stone. This will act as an artificial reflector of light improving the brilliance and eliminating the window.

Final Thoughts

Window or no window, the value of the gemstone is always subjective to the person who owns it. Some gemstone types like emeralds may purposely cut to have a windowing effect so the gemstone is more transparent and colors are displayed prominently.

You can either chose to re-cut or wear it as it is, depending on how you appreciate the stone. Don’t let by-standing experts to convince you otherwise, unless you feel the necessity to do it. However if you are planning to buy a gemstone for your ring, make sure you measure your potential gemstone against above criteria.

5 thoughts on “What is a Window in a Cut Gemstone?

  1. Pingback: Which is the Best Quality Yellow Sapphire - Amazing Sapphire
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  3. Good article, although a few grammatical errors. I am in the jewelry business and constantly reading up on this stuff to keep my knowledge current and refreshed. You did not misstate anything and were quite educational in your explanation of windowing. Thanks!

  4. Pingback: Cornflower Blue Sapphire - A Complete Buyer's Guide

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