Lesson 2: Destructive Gemstone Tests: Streak Testing
Step 3: Practical Gemology
This is a fun test if you have rough material to spare. It’s not recommended for finished gems, as there’s a good chance the gem will break. Even with rough material, choose pieces you wouldn’t mind being ruined.
As you know, most gems receive their coloring from selective absorption, the absorption and transmission of specific wavelengths of light, which can be viewed through a spectroscope. Before testing these gems, you should confirm that they don’t have any coloring material in them. You can test this by rubbing a piece against a ceramic tile. The bit of material that rubs off, the streak, should be colorless. (For example, it does not matter how dark a sapphire or garnet is, it will always leave a colorless streak unless a coloring agent has been added to it).
Streak Testing Color Chart…
Every Gemstone Is Unique - Here's How The Experts Evaluate Them
in this training-course, discover the tools, tests & valuation process used by expert gemologists for colored gemstones, opals & diamonds