Gemological Refractometer is the Essential Tool for Gemologists
Since December, I have been searching eBay for a used GIA refractometer. It is the essential tool of gemologists to identify stones by measuring a stone's refractive index. I finally managed to purchase one last week and it arrived two days ago. The first thing I noticed was that it was light; in fact, my Ipod weighs more. Under closer inspection, I noticed a few things:
The lid felt warm to the touch, indicating that it was made of plastic.
There was no serial number
It did have this label in the front
The hemicylinder was free of deep scratches (a good thing)
Did I purchase a reproduction? This piece of equipment sells on the GIA website for over $900! I immediately posted a query on the Gemologyonline.com forum, asking the experts there what they thought of my purchase. Surprisingly, I learned that modern GIA refractometers are indeed made of plastic! They suggested to test the instrument before returning. To be honest, I had already packed up the refractometer to be returned to the eBay seller, so I cracked open the package again, but this time, I would test a known stone. I chose my 5 carat sapphire.
5 carat sapphire, heated, VS, color ranging from dark blue to royal blue to light blue
I brought out my well-used grey polymer clay and made a large stand for my flashlight. I also used some to make a donut to hold the yellow filter on top of my flashlight.
FIMO donut holding yellow filter (purchased from eBay) filters out all light except 589nm which is the color of burning sodium (table salt). This provides the appropriate color of light to view the refractometer readings.
Flashlight propped up with the FIMO
A week before, I purchased a small bottle of RI fluid from eBay.
Instead of clear, it was cloudy with chunks of wax that had leaked from the rim of the bottle into the fluid. The seller insisted that it was still usable, so I gave it a try. I put a very very tiny drop on the hemicylinder and gently placed my stone on top of the drop.
Here is the photo of the results:
Sapphire has an RI of 1.76 to 1.77. This clearly is not correct with a reading of just over 1.5.
However, if I dip my head down, the shadow moves lower to around 1.7. I tried to follow the published instructions but I couldn't find the blue-green band that indicates that your eyes are aligned with the refractometer. Are my poor results caused by the faulty RI liquid or the refractometer?
After discussing my results with my husband, I realize that I'm not willing to risk my $400 on a used item and would rather buy a new refractometer. However, I'm not going to buy a GIA brand, but a Gempro:
Gempro refractometer retails for $545 at Kingsley North.
It comes with RI liquid, yellow filter, flashlight, and polarizing filter.
I also learned today that the Gempro refractometer is also plastic like the GIA version. The only all-metal body refractometers were made by the GIA 20 years ago. I will be ordering a Gempro tomorrow after I have shipped out the eBay-purchased refractometer.
**Update: I did not buy the Gempro refractometer but a 1950's Rayner refractometer.