If you’ve made it through our 3-part refractometer guide for gemologists, test your knowledge of refractive index (RI) analysis with this mini-quiz. Click on the link at the end of the quiz to see the correct answers. Got some wrong? Check out the refractometer review section below.
1. Parallax is caused by
- Double refraction
- A facet not being flat
- Lenses that need cleaning
- All the above
- None of the above
2. If you use a red filter with your refractometer, you need to make an adjustment to your reading of
3. If you’re testing a gem and measured a high RI of 1.612 and a low RI of 1.608, the stone’s birefringence is 0.004.
4. A moderate-sized spinel inclusion in a spinel host gem will have a significant effect on its value.
For the answers, click here.
Parallax is an optic effect that looks like the cutoff line wavering between scale divisions. It’s caused by a non-flat facet. Parallax is a common occurrence in refractive index testing that can be confused with an indication of gemstone birefringence.
A refractometer should be calibrated at…