A polariscope is used to differentiate between singly (isotropic) and doubly refractive (anisotropic) stones. A stone is placed between two polarizing filters and the top filter is then turned. If used with a conoscope, interference figures can also be seen with a polariscope. Conoscopes are difficult to explain in words, so directions for use are not covered here. We suggest you consult http://www.gemologyproject.com. They have videos showing the use of the conoscope.Step 1:
Turn it on. You may have to attach the power cord on a table top model, or put batteries in the flashlight of a hand held model.
- Gently place your stone on the removable lense. Some people prefer to use tweezers to hold the stone between the two filters. We find this requires 3 hands, and prefer to simply rest the stone on the removable lense.
- Turn on polariscope. Look through the upper lense of the polariscope. Rotate the top lens until it is in the crossed position (dark.) Rotate removable lense exactly 1 full rotation.
- Stone stays dark = Single Refractive (isotropic)
- Stone stays light = AGG
- If you see anything else (blinks or snake bands), take the next step:
- Return the polariscope to the dark (crossed filter position.) Use the stone holder to turn the stone to its lightest position. Then looking down through the top filter, quickly turn the top filter 1/4 turn. Results:
- Stone becomes NOTICEABLY lighter = SR- ADR
- Anything else (stays the same, gets darker) = Double Refractive
- Compare your findings to the chart below
- Isotropic (single refractive or SR)-stays dark throughout a 360° rotation.
- Anisotropic (double refractive or DR)-blinks 4 times,2 light and 2 dark during a 360° rotation .
- Aggregate (AGG)-stays light throughout a 360° rotation
- Anomalous Double Refraction (ADR) -twinkles instead of blinks. Looks like double refractive but is single refractive
- ADR is when a stone looks like it might be blinking, but really is just showing lighter where the stone is thinner or where there is a veil or weakness in the stone. Garnet and diamond sometimes display this phenomena. Tips! Be careful with using the polariscope for red / purple / orange stones. They often give confusing ADR results. Use your dicroscope or refractometer to confirm. Stones with very high RI's can also give misleading results.
- Zoisite (Tanzanite)
- Mossenite (Syn. Diamond)