The Refractometer: How To Use a Refractometer to Help Identify Rocks, Minerals and Gemstones

There are a number of different instruments available to help you in gemstone identification. But once you learn how to use it, a refractometer on its own can often provide you with enough information for accurate identification of many different types of gemstones.

How To Use a Refractometer

The first, and most important thing to keep in mind when using a refractometer is making sure that you have a good source of light. What you need is a source of:

  1. White Light (halogen lamp)
  2. Monochromatic yellow light (filters out all light except yellow)

There are lamps available that are able to provide you with both types of light sources. Many refractometers have a light source built, so no need to purchase an external light source for these.

The refractometer has a scale that shows the refractive index of a stone. The scale can measure as low as 1.35 and as high as 1.80, which is more than enough scale for most gemstones.

  1. Carefully place a small drop of refractive index liquid on the hemicylinder.
  2. Place the stone on the hemicylinder
  3. Place a white light in front of the refractometer
  4. Look through the eyepiece and note the measurement on the scale
  5. Repeat the process using a yellow light to determine if single or double refracting stone

How To Care For a Refractometer

The hemicylinder, which is the glass part that you place the stone on, can scratch very easily. If this glass scratches, it’s possible that you will not be able to get accurate readings from your refractometer.

If the contact liquid dries or evaporates, it can leave behind little crystals on the hemicylinder. To remove these, simply moisten the crystals by adding a small drop of the liquid, and then carefully wipe the glass.

If you wipe the hemicylinder before dissolving the crystals, you risk scratching the glass as the crystals are abrasive.

If you know that the refractometer will not be in use for quite some time, then you can apply a small amount of Vaseline on the surface of the hemicylinder. This will help prevent tarnishing over time which can affect the functionality of the refractometer.

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