These include the loupe, tweezers, dichroscope, ultraviolet light torch, polariscope, the Chelsea Colour Filter, specific gravity, and neodymium magnets.
In the fourth and final edition of the series, it’s time to explore some of the most informative instruments available today.
Though not quite travel friendly, a combination of the refractometer, spectroscope, and microscope often provides enough information to give a strong indication of a gemstone’s origins and identity.
The refractometer is one of only two gemmological instruments that produces a numerical value as a test result along with the specific gravity test.
This makes it possible to reference the result against a set of constants for gemstones and narrow down the possibilities of what you are testing.
As is often the case with gemmological testing instruments, understanding the principles behind the refractometer is essential to accurately interpret the results.
As light travels through air then enters a denser medium, for example as a ray of light passes through a gemstone, it bends and slows down.
The degree to which the light bends is directly related to the density of the material. This bending of light is known as refraction.
In some gemstones, the ray of light will both bend and split into two rays.
Each of these rays will have its own refractive index that is determined by the direction the ray is travelling in the gemstone.
Whether a gemstone has one or more refractive indices, the values are generally quite consistent within each gemstone species.
This leaves you with useful information about the optical nature of the gemstone being studied.
Interpreting the information is ‘easy’; however, obtaining it in the first place can be difficult for the inexperienced.
Testing a gemstone on the refractometer can be challenging for some at first.
As always, practice is the key!
Spectroscope
Another instrument that is often difficult to master is the handheld spectroscope.
As the name suggests – this instrument splits white light into its seven spectral components of red, orange, yellow, green, blue, indigo, and violet.
When using the spectroscope, a gemstone is placed between the light source and the instrument.
The spectrum produced in the spectroscope allows the observer to distinguish which parts of the spectrum, and therefore wavelengths of light, are absorbed by the gemstone.
Used in the fields of both gemmology and chemistry, the spectroscope is a window to the chemistry of a gemstone.
More specifically, it offers an insight into the elements that are responsible for the observed light absorption.
As each element has a characteristic absorption pattern, the spectroscope can be useful for identifying which elements are present within a gemstone.
For example, a gemmologist may observe chromium in ruby or iron in an almandine garnet.
Microscope
In the conclusion of the Tools of the Trade series, it’s fitting that we should reflect on the instrument which so often sparks a gemmologists love affair with the science.
The microscope acts as a portal to a new world, offering interesting scenes of inclusions in gemstones that can produce captivating photomicrography.
Additionally, this high power of observation can reveal valuable information, such as a gemstone’s country of origin or any treatments it may have been subjected to.
With a dedication to learning to use the gemmological microscope and its different lighting techniques, this one instrument might rightfully be considered the most valuable in a gemmologist’s arsenal given the sheer volume of information one may gain.
Finally, it’s important to note that the instruments themselves are less than half the requirement for gemstone testing.
The knowledge gained in gemmological studies and an understanding of how results are obtained and what they mean is essential to accurately identifying gemstones, and indirectly, their value.
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