Every faceter should know and use the white paper test. In particular, novice gem cutters and those with little experience buying gem rough should familiarize themselves with it.
Basically, this test allows you to easily approximate the color and saturation a piece of rough will show when cut.
How to Conduct the White Paper Test
Before buying a piece of rough, check it in the following manner:
- Put it on a white piece of paper in normal daylight, preferably, or mixed light (incandescent and fluorescent).
- Make sure there’s no light behind the rough. Get it away from any bright light source (like a dealer’s halogen-lit display cases).
- What you see in good average daylight comes close to what the stone will look like when cut.
If the stone looks black with very little or no color, you don’t want it. (Of course, if you insist on buying it, read my guide to dark saturated rough gems).
Take a look at the tourmaline crystals in the picture below. These pass the test easily. You can see good color.
You want to buy rough that will show at least some color flash when you do the white paper test.
It’s also a good idea to test rough under incandescent and fluorescent lighting, too, if possible. You can then see what colors the cut gem will show under those lights. This is particularly helpful if you’re buying color change gems like sapphire or spinel.
How to Improve Your White Paper Test Skills
Get into the habit of testing whatever rough you’re cutting in your lab or workshop. (You’ll have much more control over your lighting, too). Then, compare your approximations with the actual results after cutting. This will give you more experience, which will help significantly the next time time you buy rough.