Question 1: Parallax is caused by
- Double refraction
- A facet not being flat
- Lenses that need cleaning
- All the above
- None of the above
Question 2: If you use a red filter with your refractometer, you need to make an adjustment to your reading of
- – 0.005
- + 0.589
Question 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.
Question 4: A moderate-sized spinel inclusion in a spinel host gem will have a significant effect on its value.