How are Gemstones Identified?
How are Gemstones Identified?
For hundreds of years Gemologists have been discovering, cataloging & identifying new gemstones but what techniques have developed during this time to uncover the stones secrets?
Unfortunately it would take many blog posts, books and articles to explain the science of Gemmology however here is a brief and simplified explanation on how gemstones are tested. This is not an exhaustive list but a beginners guide to some of the tools used.
Synthetic stones can be just as fascinating as natural stones. Rubies were first synthesised in 1902 by Prof. A.V.L. Verneuil, a process called 'flame-fusion'.
The Gemologists Tool Kit
Gemmology is a science looking at the origin of gemstones and how we take those gemstones and fashion them in to jewellery and ornaments.
A Gemologist's hand-held toolkit consists of a 10x lens or loupe, Dichroscope, Polariscope, Spectroscope and Chelsea Colour Filter (CCF). Additional tools include a Refractometer and measuring equipment.
Please note this is a taster Gemmology and could be helpful for anyone who is interested in studying the subject.
The 10x Loupe allows you to observe the colour, shape and cut of a gemstone alongside observing its transparency, lustre and optical effects.
Firstly identifying the colour of your gemstone is the first step, for example you don't see a 'red' Iolite. The cut and shape of a stone can give you a clue to its identify, Emeralds for example are brittle they are usually fashioned with cut-off corners in a rectangular or square shape also known as an 'Emerald Cut'. A loupe is used to identify inclusions within the stone and observe external features such as fractures and abrasion.
A Dichroscope put simply separates out polarised rays helping the Gemologist to see if the gemstone has any sign of colour change or shade difference. Separating out these rays allows further insight into the gemstones because only certain types of gemstones display these colour changes.
A Refractometer measures the Refractive Index (RI) of a gem material. Each gemstone has a slightly different (sometimes overlapping) RI, this can help to narrow down similar looking gemstones. It is not always a diagnostic test, as with all of these instruments often they are used in conjunction with one-another.
Synthetic gemstones can sometimes give the same results as the natural gemstones they are trying to mimic.
A Polariscope can be used on transparent stones, the stone is placed between two polarised filters. These filters set at a crossed position which provide a sensitive test for singly or doubly refractive gemstone. This instruments allows you to test the optical character of a gem material.
This hand-held Spectroscope is used to spread out the white light spectrum - it looks like a rainbow.
When a gemstone is placed in between the light and Spectrometer its Spectrum is revealed. When light passed through the coloured gem material parts of the spectrum is missing, it has been absorbed by the electrons in the gem material.
While not all stones produce a strong spectrum it is another handy tool for distinguishing some materials from others.
Chelsea Colour Filter
The Chelsea Colour Filter was manufactured by 'The Gemmological Association of Great Britain' aka Gem-A. The filter was originally designed to identify Emeralds. An Emerald seen through the filter glows a deep red, however modern Emerald simulants can mimic the same results. The CCF can be used on Green, Blue and Red stones with various results. Another excellent tool which can be used alongside the other instruments.
Specific Gravity (SG)
Finally for an unmounted solid (no drill holes preferably) stone, measuring its Specific Gravity can give us another method to identify the gem material.
To calculate the SG you need to compare the weight of water with the weight of the object in the air. Each material has approximate SG's which can further assist the identification of a gemstone.
All of the instruments and tests mentions are just a short list of the tools used to identify different gem materials.
Written by Tiffany
Tiffany is the owner of Mayveda Jewellery. and is currently studying Gemmology at 'The Gemmological Association of Great Britain' aka Gem-A.