ISG Fun with the Refractometer

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PinkDiamond
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ISG Fun with the Refractometer

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We have information on how to use the refractometer already, but it never hurts to refresh peoples' memory, and you never know what tips you might find in each article, so here's a pre-Tucson refresher I hope you'll find useful whether you're going or not. I also hope you enjoy RJ's tongue-in-cheek commentaries. He always gives me a chuckle or two. :lol:

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10 January 2020

ISG Fun with the Refractometer

Let's start getting ready for the Tucson Gem Shows!

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For those of you who missed this newsletter edition last time, I thought we would offer a review today in preparation for the upcoming Tucson Gem Shows.

First, if you have ever wondered what a refractometer looks like with its guts out, just look at the image at left. Here are the inner workings of the ISG Refractometer.

If you look closely at the lower right side you will see two screws with red coloring. These are your calibration screws and they must be in exactly the right position. If anyone has ever purchased one of those cheap US$90.00 (or less) refractometers on eBay and wondered why your readings were skewed, its because the company did not actually calibrate the refractometer...they just screwed the parts together and sold it on eBay. To get proper readings these calibration points must be carefully positioned and glued tightly.

The manufacturer of the ISG Refractometer thinks I am clinically OCD about calibration. I personally spot check our refractometers coming into the office to make sure of the calibration. If I find one off...well, you know how I can get about these things. We are very careful about calibration, something those cheap eBay sellers are not.
ISG Quick Guide to Use the Refractometer

For those who are just getting started, or perhaps need a review of how to properly set up your refractometer for reading, here are eight steps to remember, along with a slide presentation below to help you understand the issues.

1. Open the top of the refractometer and make sure you have an operational light source.

2. Very carefully place the refractive index liquid on the stage of the unit, making sure that your dropper or push top (depending on what kind of RI liquid dispenser you have) does not touch the hemicylinder Although the ISG Refractometer has the new cubic zirconia hemicylinder that replaces the very fragile old leaded glass hemicylinder, you still need to use caution in this step.

3. Make sure you only get a single drop of RI liquid on the stage. Too much liquid will cause your readings to become skewed.

4. Carefully place the stone on the liquid. Be careful not to set the stone directly on the hemicylinder

5. Carefully slide the gemstone over the CZ hemicylinder to the position for reading.

6. Once in place, close the lid to avoid outside light interference, and be sure to use your polarizing filter for all readings.

I have created a slide presentation below to take you through the steps.

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7. Remember that refractometers come with focus lenses that allow you to slide the lens up and down to ensure the best focus of the reading scale and more accurate reading.

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8. Be careful to wipe the RI liquid off of the refractometer. Use a tissue as this stuff is toxic, very toxic. Don't breathe it and don't get it on your skin. Breathing this stuff very long is sort of like taking a vacation in Chernobyl if you know what I mean.

Of course, there are more issues, such as not getting too much liquid and not mistaking the liquid refractive index for a gemstone reading. However, room in this newsletter is limited and we cover these topics in the ISG Gemology Tools and Techniques course.

OK, so what if you are out in the field and have no electricity and no batteries and need to take a refractive index reading. Well, I learned a little trick from the good folks at the Gem-A that works quite well. Here is the story:

The Candle Light SodiumD Refractometer Light
The monochromatic "sodiumD" light wavelength is considered the best, standard light to use when taking a refractive index. This is because refractive indices can vary in light sources, so this is the standard to use. While our candle is not going to make a true sodiumD light source, you may be surprised at just how close you can come to creating one with this method. Here are the steps.

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Step 1: Simply get a refractometer with a gemstone, candle and lighter.

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Step 2: Make sure the refractometer is of the design that allows for an outside light source to be used, as shown at left. (sorry for the brownish ding on the refractometer, this one went through the drunk driver crash into our building)

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Step 3: Light the candle and measure how far up or down you need to move the refractometer to insure the light of the candle is going directly into the light source opening.

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Step 4: Use whatever you have to in order to maximize the candlelight into the light source opening.

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Step 5: Get your Morton salt, or whatever salt you have available. Make sure it is NaCl table salt and not some exotic type salt that will blow up when exposed to a flame.

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Step 6: After letting the candle burn down just a bit, fill the melted wax area just below the flame with the table salt. Not too much as it will douse the flame and you will be groping around in the dark looking for your lighter...and that lost shaker of salt that Jimmy Buffett is always looking for in Margaritaville.

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Step 7: If you are really creative and have a diffraction grating spectroscope in your pocket, you can actually see the strong sodiumD transmission line coming out of your candle and table salt light source in the visible spectrum. At left is this light taken with the OPL Teaching Diffraction Grating Spectroscope I got from Gail at the NAJA office (it is amazing). If you want one here is the order link: NAJA OPL Spectroscope.

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Step 8: Take your reading.

The 1.553 reading of this citrine is pretty amazing to come from candlelight.

I hope you had fun with our review of the refractometer. Remember, this gemology thing.....it ain't rocket science. It is fun and rewarding regardless of what professional or hobby level you may be on. There is always something new to learn, and new gemstones to work with. Never stop learning.



Robert James FGA, GG
President, International School of Gemology
To learn more about the ISG world-class programs in gemology and jewelry appraisal, click here: https://schoolofgemology.com/ We have maintained an Accredited A+ rating with the Better Business Bureau since 2006.

©2020 International School of Gemology. ALL RIGHTS RESERVED. We encourage sharing and caring throughout the industry as long as all copyrights are left intact.

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International School of Gemology
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Helotes, TX 78023
PinkDiamond
ISG Registered Gemologist


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