How to Make a Pinhole Refractometer

Distinguishing an aquamarine gem from a blue topaz or a synthetic blue spinel is not easy. The trouble is aquamarine is by far the most valuable gem. So if you can't distinguish it from inferior stones, you could be in for an expensive and disappointing mistake. The same problem arises with other precious stones. Gemologists have a selection of tools to help them identify the type of stone they are examining, which you can also learn to use. Among them is the refractometer. Refractometers test a stone's ability to bend light by measuring the angle created by a ray of light's path before and after it passes through a gem. Every stone has a unique refractive index, so if you can measure the refraction index, you can identify the stone (see References).

Things You'll Need

• Toothpick
• Card
• Tweezers
• Refractometer eyepiece
• Refractometer scale
• Gem

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Instructions

1. • 1

     Pierce a small aperture into the center of a piece of card with a toothpick or sharp scissors (see References).

   • 2

     Place the gem you are examining on the refractometer's bubble and place the refractometer scale behind it. You can hold the gem in place with tweezers or by placing some contact fluid on the bubble and holding it above the scale (see References).

   • 3

     Hold the card close to your eye and look at the gem and the scale through the pinhole aperture (see References).

   • 4

     Look for a dark line on the refractometer scale and write down the reading. This is the stone's refraction index. Then compare your reading with a published list of refraction indexes (see Resources). This will guide you in identifying the stone.