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A piece of rock crystal or colorless quartz cut into a wedge shape can help a gemologist conduct optic sign tests with a polariscope. “Quartz – Rock Crystal” by Lucky Lynda is licensed under CC By 2.0

A piece of rock crystal or colorless quartz cut into a wedge shape can help a gemologist conduct optic sign tests with a polariscope. “Quartz – Rock Crystal” by Lucky Lynda is licensed under CC By 2.0

Question

I’m reading the International Gem Society (IGS) polariscope guide and I noticed the quartz wedge in the accessories section. I have never seen one before. Although I’m a gemologist, I’m ashamed to tell you I don’t know how to make or use a quartz wedge. I have some very clean quartz crystals and would love to give this a try.

Answer

Making a quartz wedge accessory for your polariscope is not too hard if you have some lapidary skills. Start by sawing a rectangle along the long direction of the crystal. Make it approximately half as thick as it is wide. (The proportions don’t have to be precise.) Next, taper it to a point like in the picture below.

wedge

You can also buy a quartz wedge online or a plastic substitute, too.

You’ll find instructions for using the quartz wedge in part 2 of our polariscope guide. Basically, after finding a gem’s optic sign, you can use a quartz wedge and your polariscope to determine whether the sign is positive or negative very quickly. Some additional accessories can help. A jeweler’s third hand or a stone holder from a microscope can secure the gem so you can have your hand free to use the quartz wedge. If you don’t have these, you might need to recruit an assistant.

Remember that quartz wedges are classed as “fast” or “slow.” Part 2 of our polariscope guide has instructions for using both. If you don’t know what kind of quartz wedge you have, test it with a gem of known optic sign.

Best Wishes,

Donald Clark, CSM IMG

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