Stephanie asked on our Facebook page “Greetings…Can you please tell me what a WINDOW is in a stone, and maybe show me an example? I hear you folks refer to it often. Thank You”
From our Director of Gemology:
A window in a gemstone is seen when the pavilion (bottom) of the gemstone is cut in a way that light passes through a gem rather than being reflected back. The angles of the pavilion facets allow light to ‘leak’ out of the bottom instead of being reflected back up through the stone. The less than optimal cutting creates a stone that is less brilliant than a stone cut to the best angles to return as much light as possible. A shallow stone can also be the cause of a window because it does not provide the depth for the correct angle of facets to reflect light back in an optimal way.
Diamonds are cut to very specific dimensions to reflect as much light as possible, however colored gemstones are sometimes cut to yield the highest carat weight possible. This can mean the same precision of the pavilion angles is not taken into account. The gem cutter is balancing the size of the gem he/she can produce with the possible beauty of the finished gemstone and making a call on how to facet the stone. Sometimes he/she decides to keep carat weight sometimes the cut is for maximum brilliance.
For example; if a stone can sell for $100 per carat and the cutter’s options are a 10ct stone with a window or a 7.50ct stone with better angles and no window they may opt for the bigger stone, because it would likely sell for more money. That is if the size of the window is acceptable and does not diminish the value of the gem.
One easy way to spot a window is if you look at a gemstone straight on through the table and see what appears to be a lighter center with a darker ring around the outside – that lighter area is a window. Another thing you can try is to see if you can read text clearly through a gemstone. Normally facets would distort the text but lack of faceting or large facets at poor angles can yield a window you can actually see text through.
Windows are one of the characteristic of cut that can affect the value of a gemstone. A small window might be acceptable, no window is optimal, but not always practical. Remember that cut affects the brilliance of the stone, the amount of light reflected back out of a gem – a bright lively stone is almost always preferable to (and more expensive than) a bigger stone that is not bright.
That said having a stone with a window is not a bad thing. Emerald cuts for example are cut to see the color and clarity of the stone not the brilliance. Gems are a lot like art – beauty is in the eye of the beholder. If you have a gem and its unique color and beauty speak volumes to you, then you should be happy with your gem regardless of it’s value or cut.
Thanks Stephanie for taking the time to ask a question, we hope you find this answer helpful.