The Jackson’s Gems Standard
We refuse to sell “dead” stones. At Jackson’s Gems, we meticulously evaluate and test the optical axis of every piece of dichroic rough—particularly our Tourmaline inventory—before it is listed for sale. You can cut with confidence knowing the orientation has already been vetted by master cutters.
1. What is Pleochroism?
In simple terms, Pleochroism is the ability of a gemstone to show different colors when viewed from different crystal axes.
This occurs because the gemstone’s internal crystal lattice restricts and absorbs light differently depending on which crystallographic axis the light is traveling down. Stones displaying two distinct colors (like Tourmaline and Sapphire) are dichroic, while stones displaying three colors (like Tanzanite) are trichroic.
Jackson’s Gems Insight
Since 2001, we have helped countless cutters avoid the devastating mistake of failing to accurately identify the “best” color axis of their material. This single miscalculation in geometry can instantly turn a $500 piece of rough into a $50 finished stone, which is why perfect orientation is everything.
2. Finding the “C-Axis” in Tourmaline
Tourmaline is our bread and butter, and it is perhaps the most famous dichroic gemstone you will cut. Tourmaline crystals naturally grow as striated prisms. The long sides (the width) of the crystal form the A/B-Axes, while the “ends” (the length of the prism) form the crucial C-Axis.
Because Tourmaline strongly absorbs light traveling down the C-axis, looking directly down the ends of the crystal often reveals a color that is significantly darker than looking through its side.
Technical Advice: The “Open vs. Closed” C-Axis. If the ends of the crystal are completely black (a “closed” C-axis), you must orient the table of the gem perpendicular to that axis so you are looking down the brighter A/B axes. This is the only way to keep the stone from “blacking out.” Conversely, if you have rare rough with an “open” C-axis, you have the opportunity to experiment with end-color geometry.
3. Using a Dichroscope or Polarizing Filters
You cannot effectively orient complex dichroic rough using just the naked eye. We highly recommend using a simple, handheld dichroscope to see the two (or three) colors safely hidden within the rough.
By shining a diffused white light through the crystal and inspecting it through the dichroscope, the optics will split the pleochroic colors into two distinct viewing squares right before your eyes. This empowers you to isolate the precise axis harboring the “pure” hue you want flooding the table of your finished gem.
Professional Resources: Learn more via the GIA’s Guide on Gemological Instruments, or source professional-grade dichroscopes directly from dealers like Kassoy.
4. The Physics of the “Light Path”
When you align the crystal on the dop stick, you cease being a stone cutter and become an architect. You are physically designing the light path. By deciding exactly where the table goes and charting the angles of the pavilion, the cutter acts as the architect deciding which of the pleochroic colors “wins” in the final gem’s brilliance return.
Master Tip: Advanced Zonation
For highly complex rough like Bi-Color or “Watermelon” Tourmalines, orientation is absolutely everything. You must carefully calculate the light path to ensure the color split sits perfectly balanced and centered within the pavilion to guarantee both colors remain vibrant inside the finished gem.