A refractometer is an instrument that determines the refractive index value. In my country, it is mainly used to measure the refractive index of gemstones and jade.

Refractometer structure: composed of high refractive index prism (lead glass or cubic zirconia), prism mirror, lens, ruler (inner ruler or outer ruler) and eyepiece.

The working principle of the refractometer is based on total internal reflection. The instrument measures the critical angle of a gemstone and converts the reading directly into a refractive index value.

Conditions for generating total reflection:

1. The high refractive index prism of the refractometer must be an optically dense medium

2. The gemstone to be tested is an optically rarer medium

3. The contact fluid creates good optical contact between the prism and the gemstone to be tested

Operation essentials

1. Power on, turn on the instrument

2. Clean gems and prisms with alcohol

3. Spot a drop of contact fluid (approximately 2mm in diameter) on the prism of the refractometer, illuminate with sodium light, and see the shadow boundary of the oil

4. The largest table of the gemstone is placed on the prism, and the immersion oil creates a good optical contact between the gemstone and the prism

5. Eyes close to the eyepiece to observe the shadow area and bright area and read, and the reading is reserved to the third decimal place

6. Rotate the gemstone 360° in sequence, and the experienced person can rotate the gemstone 0°, 45°, 90° for observation and reading

7. After the test is completed, push the gemstone onto the metal table and remove the gemstone

8. Cleaning gems and prisms