Of particular interest is the way in which light interacts with a gemstone, and it’s the study of this phenomenon which is often the focus of testing.
When examining an unidentified gemstone, it is the gemmologist’s job to interpret and then translate these readings in pursuit of understanding. From there, the gemmologist may piece together the clues they offer to determine which classification the gemstone they are examining belongs to.
The Loupe
The simplest and most utilised tool is the hand lens, otherwise known as the loupe.
These first lenses were certainly simple compared to today’s modern marvels. The first that can be directly traced to modern tools was a surgical loupe with two lenses created in Germany in 1876, used for medical surgery.
Since then, loupes have been widely used in the medical field for both surgery and dentistry, as well as by both the geology and gemmology community. Though many types are available, the most common is the 10x triplet.
These convenient, handheld tools magnify an object 10 times, allowing the observation of features often invisible to the naked eye.
This is essential for examining characteristics such as the quality of faceting work, searching for any damage, inclusions within the gemstone, reading laser inscriptions and more fine detail. This is the one tool a gemmologist will always carry with them when working.
As a rule of thumb, the clarity grading of diamonds is determined by the visibility of inclusions under the 10x hand lens.
When it comes to variety, hand lenses vary greatly in price and quality. For all gemmologists, it is well worth investing in a premium hand lens in order to reduce eye strain and ensure no details are missed or overlooked when inspecting gemstones, as this can always be costly later!
Along with a quality hand lens, a sturdy pair of tweezers is a must. It’s important that gemstones are handled with care, as untrained handling can lead to chipping and damage.
The Dichroscope
Also in the realm of compact tools, the dichroscope provides a test to separate gemstones such as sapphire and spinel, garnet and tourmaline, and more.
The dichroscope is, described very simply, a rhomb of optical calcite, otherwise known as Iceland spar, within a tube with glass prisms on each end. Essentially this little tool gives a clear picture of a gemstone’s pleochroism – this is the different colours the gemstone may show when viewed in different directions.
Given colour is key with the dichroscope, it cannot be used on colourless material or with any gemstones that are too light in colour to distinguish clear differences.
When a gemmologist looks through the viewing window there are two little squares visible. If the gemstone has pleochroism, the squares will be two different colours in most directions so long as the gemstone is doubly refractive.
In singularly refractive gemstones, only one colour will be seen in both squares regardless of how much you turn and view the stone.
This is useful as it enables the separation of double-refractive gemstones such as sapphire, tourmaline, zircon, and iolite, from singularly refractive gemstones such as spinel, garnet, and fluorite.
In addition, gemstones that are dichroic, meaning they show two pleochroic colours, can be separated from trichroic gemstones – those that show three.
Like most gemmological instruments it is only with the theoretical understanding of how light interacts with gemstones that one can make sense of what is being observed in the dichroscope, making education in gemmology the essential component that ties the information together.
These aforementioned few instruments are often found together in the tool bag of the field gemmologist and given their compact nature are each easy to use and versatile.
But what about inclusions? Refractive indices? The density of differences between minerals? Each individual instrument can provide a great deal of information, but so often, the identification of a gemstone is possible only in collaboration with data obtained from other instruments. One must always remember that being a gemmologist means investigating how these tools provide the information we must piece together to form the bigger picture.
In the next issue of Jeweller the examination of a gemmologist’s tried-and-true tools of the trade continues with part two.