Assign 3

Question 1

When a gem shows definite birefringence on a refractometer, this proves it is

Answer 1

Doubly refractive

Question 2

The imaginary line perpendicular to the point of where a ray of light strikes the surface of a gem is called the

Answer 2

normal

Question 3

Spectral colours that appear on the refractometer scale might mean

Answer 3

you need to use less RI fluid

Question 4

If you see a distinct shade cutoff in the refractometer at 1.80, you should

Answer 4

record the stones RI as OTL

Question 5

To get a good spot RI reading on a curved surface, how many scale divisions should the spot cover?

Answer 5

2 to three

Question 6

The most accurate refractometer spot reading method is the

Answer 6

50/50 method

Question 7

To check a spot reading for birefringence blink, you must

Answer 7

remove the magnifier and use white light and the polarising filter

Question 8

The numerical difference between a DR stone’s highest and lowest RIs is its

Answer 8

Birefringence

Question 9

When you’re testing a well polished, faceted gem and you use monochromatic light with the refractometer, you’ll

Answer 9

get a sharper reading