It was sultry summer afternoon when a beautiful dame walked into my office. She had a beautiful oval shape, bright facets, and a deep blue color. “You a Graduate Gemologist?” she asked. “That’s what the door says,” I replied as I sat up straighter. Something about her blue, faceted countenance seemed off. “Well, I have a problem…I don’t know who I am!” she exclaimed. It’s another case for CSI Gemology!
If you have read my previous two blogs beginning with www.angelacisneros.com/post/csi-gemology-part-1 , you’ll know that being a Graduate Gemologist is a bit like being a detective. Based on observation, tools, and experience, a Graduate Gemologist will take a list of “suspects” and ask all the right questions to get down to the proper gemstone identification. In Part 1, we explored the power of observation, and in Part 2, we explored various things a 10x microscope can tell us. In Part 3, we’ll delve into the fascinating world of the Refractometer! (pronounced re-fract-ah-mit-er)
Most of us are probably familiar with the idea that the speed of light travels 186,000 milesper second. When light hits an object, there is a measurement that tells us how fast light is absorbed into an object. Since there are various materials that objects are made of, the speed of absorption is also going to vary. The Refractive Index of an object is a dimensionless number that describes how fast light travels through the object. Since gemstones are made up of an individual crystal structure and chemical composition, each gemstone is going to have their own Refractive Index number!
The Refractometer is an instrument created by the Gemological Institute of America to specifically find the Refractive Index of faceted gemstones. Most Graduate Gemologist use the approx. 6” long by approx. 2” wide instrument right on their desktop. It is one of the more tricky tools to use and takes some time and help to master. If one isn’t trained properly or is not careful, one can easily get a misread of the instrument. The Refractometer also measures whether a gemstone is singly or double refractive which is an important distinction when identifying a gemstone. Here are the Refractive Indexes of some gemstones:
· Diamond: 2.417 Singly Refractive
· Sapphire/Ruby: 1.76 to 1.77 Doubly Refractive
· Emerald: 1.577 to 1.583 Doubly Refractive
· Amethyst: 1.544 to 1.553 Doubly Refractive
Using the Refractometer is like getting a break on the case. The suspects narrow down by a lot, and in a simple case, this information along with information gathered from observation and the microscope will be enough to give a definitive answer. Sometimes, it’s not so easy! Next week, I will talk about other instruments we use!
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Photo credit: gia.edu