Before grading, make sure you’re dealing with natural, gem-quality corundum — rubies or sapphires — rather than lab-made material or entirely different gemstones. You’ll need some basic gemological equipment to measure the physical and optical properties of your gems.
A simple loupe is the best first tool to use when identifying gemstones. Look at the stone’s inclusions and growth planes. Are these consistent with natural corundum? A loupe can also help you determine if a gemstone has been faceted well. Although not a definitive test, synthetics and imitations typically don’t receive quality cuts.
A microscope can give you a closer look at the gem and its inclusions, helping you identify it.
The next set of properties you’ll need to analyze in difficult separations are refractive index, specific gravity, and light absorption spectra. To measure these, you’ll need a refractometer, a modified or specialized balance or electronic scale, and a spectroscope. Make sure that all properties of your test stone are consistent with those of natural ruby or sapphire.
These tools, in particular loupes and microscopes, can also help you identify some common corundum treatments. They can even help detect if a ruby or…