RosGem Precision Pocket
Refractometer
Model RFA-322
With the highest-precision scale, this may be the best portable refractometer found on the market today.
• RI readings from 1.300–1.81
• Measures 4½" long x 2½" high x 1¼" wide
• High-precision scale with readings up to three decimal places
• Focusable eyepiece with polarizing filter
• Hinged cover permits easy examination of large pieces
• Sharper scale with clearly marked gradations
between major numeric values for easier and more precise readings
• Slide with diffuser for white light and interference monochromatic filter—simply move the slide to the left for monochromatic light, to the right for white light
• Comes with protective leather travel case
The refractometer measures the angle at which light rays bend (refract) as they travel through a substance, and provides a numerical reading (RI or Refractive Index) from a scale you see when you look though the eyepiece. Generally, the higher the RI, the more brilliant the stone. Since the RI differs for every stone, the measurement provided by the refractometer provides the identity of most stones, although it won’t distinguish between natural gemstones and their synthetic counterparts. It is used most easily with stones that have at least one flat, polished surface (a “spot” method can be used for cabochons, but this is a little more difficult).
The major shortcoming of most refractometers is that they will not work for stones with a very high RI, such as diamond, certain diamond imitations, and certain varieties of garnet. In addition, the stone must have a good polish; you cannot use a refractometer to identify rough stones or stones that are badly worn and lack a good polish.
