How Do I Use a Gem Refractometer?

Clean the gemstone to be tested by dunking it in warm, soapy water, using mild detergent. Do not leave the gemstone soaking in the water for more than a few seconds. Most gemstones have treatments to enhance color that can be affected if left in water too long.

Dry the gemstone thoroughly with a paper towel or lint-free cloth. Ensure the gemstone surface to be tested is dry and clean with no fingerprints that could contain oily residue. Do not use chemicals to clean or dry the gemstones to be tested, as any residue to could cause the refractometer to give an inaccurate reading.

Place the refractometer on a table in a well-ventilated area. Open the refractometer's top cover. Inspect the glass prism plate in the center of the refractometer for dust or residue left from previous measurements. Wipe clean gently with a water-dampened cloth. Remove any old, hardened refractive index fluid crystals by rewetting them with the fluid, allowing them to dissolve and then wiping them away with the damp cloth.

Deposit a few drops of refractive index fluid onto the refractometer glass plate prism with a toothpick or glass rod. Set the smoothest, largest surface of the gemstone to be tested down into the refractive index fluid. Press it down into the fluid to ensure proper contact. Do not touch, smell or ingest the toxic fluid at any time. Use a toothpick to move the gemstone into position. Close the top cover of the gemstone refractometer.

Place a flashlight or other strong light source as close as possible to the light entrance socket in the back of the refractometer, as the internal scale reads best in strong light, preferably sodium light. Sodium equivalent LED light sources are available. Turn on the gemstone refractometer to be used.

Look into the eyepiece at the front of the refractometer. Focus it by pushing it in or pulling it out as needed. Observe the demarcation line created by the gemstone under examination. Note where it crosses the refractive index scale superimposed in the viewing field. Write down the number on the scale. Compare this number with a chart of gemstone refractive index numbers to identify the gemstone.

Open the top cover of the refractometer and remove the gemstone, using caution not touch the refractive index fluid. Repeat Step 1. Clean the glass prism plate as in Step 3.