Recutting Colored Gems- Closing the Window

May 19th, 2012 by James L. Sweaney, CGA, FGA. GG

Natural colored gemstones come from rare mineral crystals that are found within the earth’s crust. Mother Nature “cooks” various ingredients according to her own unique recipes into crystals of different sizes, shapes, colors and physical properties. For centuries, man has sought out and fashioned these treasures into dazzling objects of beauty and value.

Because of their great rarity and value, gems have traditionally been sold by weight. As a result, gem cutters usually cut to retain a maximum amount of weight from the rough material rather than to craft the most beautiful gem.

The color change sapphire shown below is what we refer to as “native cut”, meaning the gem was cut in it’s country of origin for weight, not beauty. We liked the color but the stone just wasn’t very lively.

1.63 ct Color Change Sapphire, top and side view before recut

Note the top view – the center of the stone is dull and doesn’t reflect light very well. This is because the angles in the center of the pavilion (bottom portion of stone) are too shallow to capture the light coming into the stone and reflect it back to the eye. We call this a window, meaning that light escapes thru the bottom and you can see thru the stone.

The side view shows that the pavilion is off center and is somewhat rounded. This is weight retention that you pay for but doesn’t really provide any benefit of beauty or apparent size.

1.45 ct recut Sapphire

Since the crown of the stone was pretty well shaped, we chose to recut the pavilion only. Our cutter was able to close the window by centering the culet (point of stone), removing the excess weight and correcting the angles so that the stone captures light more effectively. We were able to achieve a much better cut without doing more radical surgery- since we didn’t touch the girdle (outer edge), the apparent size of the stone is the same. The gem now has a brighter more balanced appearance and the color shows better.

In this instance, to close the window, we lost about 11% of the original weight, and of course, we had to pay our cutter. Our rule of thumb to attempt a recut like this is 10-15% weight loss. If we think we can improve the brightness or color appearance, the trade-off of beauty for weight is worth it.

Visit our Gallery of Gems or come by our shop- as well as offering fine stones for sale, we provide full recutting and gemstone repair services. We’ll be happy to show you how cutting affects the beauty and value of gems. You’ll see the difference fine cutting makes.

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One Response to “Recutting Colored Gems- Closing the Window”

  1. Jen Says:

    Hi- i have a pretty amethyst ring, and I love the cut. I do need the stone recut or polished, as the edges are dull and really need refining. Can you tell me how long it might take and how much you charge? I have tried to take pictures of it, and I can’t get a decent shot. Its a small stone but not tiny, maybe half an inch across. Thanks- Jen

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