Sunday, March 4, 2012

Gem Testing -- What's for real?


The primary objective of gem testing is identification of the gem species. A red gemstone may be a ruby, spinel, garnet, tourmaline, CZ or paste etc. Stage two is to ascertain whether it is manmade (yes or no). Stage 3 is whether it is a natural/synthetic stone that has been treated in some way to enhance its value, such as by heating, dying, fracture filling with glass or oils. Gem testing is lots of fun and keeps gemologists in a job. The difference in value of a good quality 10 carat natural ruby and a synthetic one could be $20,000.

Gemstone enthusiasts should always carry about a small Gem Testing Kit which takes up little space but is very useful. Mine is contained within an old Drum tobacco tin, milde shag it says, and it measures ca 13.5 x 7.5 cm and 2.5 cm thick. What to put in it? It is amazing what you can squeeze into such a small space. I shall list what I have:
A loupe, having both 10 & 20X magnification. A Chelsea color filter. A homemade dichroscope 2.5 cm long made from a microscope lens and calcite rhomb. A small Rutland polariscope. Three light sources, including a tungsten incandescent pen light; a Pen light with white and blue LED; penlight with white LED and red and UV blue laser light. A pen with steel scratching point at one end and strong neodymium magnet at the other. Two gem tweezers and a length of string plus several needles and a hat pin. How to use any or all of this gear? This is explained in my Helium articles on gem testing listed in the RHS column. Why not start with "How to identify a loose gemstone"

Useful links to various gem and gemology websites including Gem Testing Labs and Gem Schools is contained at the GemologyOnLine website.