By Joe Henley - May 24, 2022
Many will have noticed that in our videos and photographs, we will usually show our rough stones on white paper. It may seem like a trivial thing but placing a stone on a white background can be an important tool in assessing if the rough is too saturated and to show how the rough will look once it has been faceted into a gemstone. The name given to this process is called the “white paper test” (WPT).
The methodology for using the white paper test ranges from simply putting the rough on white paper, to looking at the rough on white paper in different types of light (natural, warm, and cool), to putting the rough on white paper and walking around both indoors and out or putting the rough on white paper with the sun at a 45-degree angle. Over the years, I have used all these methods and have found them quite helpful when evaluating rough.
But for the reader, who is likely both reading this article online and buying their rough online, is it just as simple as having a dealer place a piece of rough on white paper and deciding from that alone the color and saturation of the finished gem? Unfortunately, it isn’t.
While helpful, the WPT does have limitations. Some rough, particularly some species of garnets and tourmalines, can have thick skins that mask a more open color. Another shortcoming of the WPT is that it often conceals zoning in a stone. Yet another is how easily the test can be deceiving for rough being shown online.
One consideration when looking at an image of a stone on white paper taken outdoors is the photo’s geographical location. I am always amazed at the difference in color and saturation of a stone photographed near the equator, i.e., East Africa, as compared to how it looks in-hand in North America. Near the equator, the sun is overhead and it’s intense. A stone that is on the border of being too dark in an image taken in East Africa will almost certainly be too dark in hand.
Another thing to watch for is when the stone is underneath a bright light source, like a lamp.
At the right angle, the light from the lamp can ‘bounce’ off the white background, making the stone appear more open.
Also be aware of stones photographed on windowsills.
There is something about the way that a windowpane concentrates the sun’s rays that results in a dark stone appearing lighter.
Speaking of concentration, I would not have any confidence looking at an image or video that had the stone(s) on a metallic or reflective surface.
In this scenario, the reflective surface is used to bounce light through the stone, masking an otherwise dark stone.
To help illustrate these points, here is the stone I manipulated with different light sources for this article.
I’m the first to say that a dealer has the right to show their stones in the best possible ‘light’. This is the driving force behind why we use clear plastic baggies to show our rough with transmitted light. But I also think it’s critically important to show the vast majority of rough stones on white paper, at least for a few seconds in a video or with a still image.
The gem trade is ancient and full of tricks and traps to be aware of. I hope this brief article is helpful in avoiding some of the more common ones.
Here are a few images I captured on social media of someone using many of the tricks I mention above
Using a metallic reflective surface
Using a cell phone light (common in the developing world) Notice how dark the stones are on the left when not directly over the light source.
This image is almost comical for accessing the color of a stone. That’s one bright light source!
Please let me know if you have any questions!