Putting Simple Gemological Knowledge to Use in the Field
A number of years ago, the owner of All That Glitters attended a well known outdoor antique market. Just in case some antique jewelry of interest was found, Mr. Brown took along the Rapport Diamond Report, dichroscope, charts of the Refractive Indexes of gemstones, his GIA Refractometer, thermal conductivity diamond tester, millimeter gauge and loupe. The day was to be spent looking at antiques, but if some piece of jewelry tweeked his interest, there were a few gemological instruments at hand, or at least, in a knapsack.
A large orange gemstone set in a ring was discovered and said to be a Topaz. The dichroscope showed slight dichroism, so this was either natural or synthetic mineral. In utilizing the Refractometer, the reading indicated that this gemstone was Citrine and not Topaz, and the gemstone/ring was no longer of interest. Had the average person purchased the ring as having a Topaz center stone, they would have overpaid and perhaps never discovered the issue. (In a discussion with a local well known gemologist/appraiser, a similar story was recently told. This associate of ours was talking to a woman who thought she had an Imperial Topaz but his testing, as well as GIAs Lab, indicated that it was Citrine. Visual inspection by those with knowledge in the field could tell that it didn't look right for a Topaz and was certainly not the color expected for Imperial Topaz).
This particular antique show was visited in another year, but no gemological equipment accompanied Mr. Brown. In one booth, was this small carved transparent monkey about 2 inches high, well executed, with a polished stomach. In the stomach area, was an embedded insect. The dealer indicated that it was amber. If Amber, this object d'art was a must have! Being suspicious that this could be plastic, Mr. Brown did not want to make the purchase and then have to return it should the item not be Amber after testing in the All That Glitters office. Improvising, Mr. Brown visited a nearby food stand where he obtained a plastic cup and a number of salt packets. The cup was filled with water and the salt was added and dissolved in the water. Amber will float in heavily salted water; plastic will sink. The salted water was taken back to perform a non-destructive and simple test. The monkey was gently placed into the water, and it sank to the bottom. As Mr. Brown had suspected, this was a piece of resin or plastic, and somewhere along the way, was created to deceive. The dealer was told of the issue with the identification.
There was another case where Mr. Brown had visited a pawn phop in NH. Looking at some diamond rings in the case, Mr. Brown used his thermal conductivity tester which could differentiate diamond from CZ or other 'simulants'. One of the rings tested as non-diamond and Mr. Brown brought this to the attention of the owner of the shop. Note that the older diamond testers have been replaced with updated versions since new products have entered the market. Diamond coatings on items may soon be a problem in some cases.
posted by All That Glitters at 10:47 AM
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