What is the White Paper Test?
The white paper test is something every faceter should know and use, this is particularly true for a new cutter or somebody who does not have a lot of experience buying rough. It is essentially an easy way to get a close approximation of what (color and how saturated) a piece of rough will cut like.
To do the Test
Take a piece of rough you want to check and put it on a white piece of paper in NORMAL daylight.
No light behind the rough, and get it away from any bright light source (like a show dealers halogens in their cases) try to make sure that it is mixed light (incandescent and florescent).
Left: As you can see the Tourmaline crystals in the picture easily pass the test. You can see good color.
What you see in good average day light is fairly close to what the stone is going to look like when it is cut.
If it the stone is black looking with no (or very little) color, you do not want it.
You want rough that will show at least some color flash when you test it this way. Also, it is a good idea to look at the rough this way under each type of light (incandescent and florescent) and check to see what color(s) it is and how it looks, especially if you are buying Sapphires or Spinels.
A good habit to get into is to do this test on rough you are cutting and then compare the results, it will help you when it comes time to buy rough in a big way.