WHAT ARE THE TOOLS USED IN GEMMOLOGY?
Before a piece of Fine jewelry can be brought to life, there are several steps to follow in regards of the sourcing of raw materials. From Gold to Gemstones, a thorough set of processes are carefully followed to ensure the best quality.
To identify a gemstone, it is necessary to follow several steps each corresponding to the use of specific instruments.
First step: make sure that the stone is not a compound stone. Then, using the polariscope, specify if it is isotropic, anisotropic, or if it presents anomalies. Then determine, using the refractometer, its refraction index.
The microscope or a loupe is then used to study the impurities and inclusions in the stone. A dichroscope or spectroscope may be needed to analyze more complex cases. Finally, it is useful to measure the density if the necessary means are available.
Table of content:
- WHAT IS A POLARISCOPE?
- WHAT IS A REFRACTOMETER AND HOW TO USE IT?
- WHICH LOUPE DO I NEED?
- WHAT IS THE BEST BINOCULAR MAGNIFIER?
- WHY SHOULD I USE A DICHROSCOPE?
- WHAT IS A SPECTROSCOPE?
- WHAT IS THE MOST FAMOUS GEM FILTER?
- WHAT DOES THE ULTRAVIOLET LAMP DO?
- WHY USING DENSE LIQUIDS?
- WHAT GEM TESTER DOES SMART ARTS JEWELLERY USES TO CHECK CVDs?
- WHAT ARE THE BENEFITS OF A DIAMOND 360 DEGREES PHOTOGRAPHY SYSTEM?
WHAT IS A POLARISCOPE?
This device, which makes it possible to recognize isotropic gems, consists of two crossed polaroids, between which the stone is examined. By turning the stone, we see it light up, then go out in the case where it is anisotropic. On the other hand, it remains obscure if it isotropic or amorphous. Sometimes, we observe gray areas that move when we do move the stone: it is then a question of internal tensions in a glass or a melted transparent matter.
Example: synthetic spinel. This phenomenon is sometimes observed on garnets.
A good polariscope should be large enough to accommodate finished pieces of fine jewelry, while holding the object to be examined in the dark.
WHAT IS A REFRACTOMETER AND HOW TO USE IT?
Each gem has one or more characteristic refractive indices which allow it to be identified.
The refractometer provides the exact measurement.
After placing the stone to be examined on the transparent part of the refractometer (a special liquid facilitates the contact between the two), we observe through eyepiece graduated scale clearly visible. On this scale appear: either a dark area and a bright area, i.e. a bright area between two dark areas.
The number(s) corresponding to these limits give the refractive index of the stone.
Solid and compact, the refractometer nevertheless has a very fragile part: the transparent one. We must therefore be extra careful:
- place the stone delicately on the glass table;
- avoid pressing to hard whilst taking readings (if you examine a small stone, it will bebetter to use tweezers);
- remove, using a blotter, any excess liquid which, on drying, would leave crystals that can scratch the table;
- gently wipe the table, once the observation is finished, with a clean buff;
- in the event of prolonged non-use, coat the glass with petroleum jelly. If he starts to be frosted, rub it delicately with a cotton pad soaked in polishing red, diluted in water.
Two principles, finally, must be retained in the choice of a refractometer:
- that it gives the clearest reading;
- that it has the most robust glass table.
If we want to obtain very precise measurements, we must:
- illuminate the device in monochromatic light or use a filter on the eyepiece yellow or polaroid;
- find the position of the stone on the transparent part which gives the best read.
Some imitation glass stones do not give a shaded area on the refractometer. Indeed, the thin film which covers them does not have the same refractive index than that of glass. This is a manufacturing accident in the most cases, but it has recently happened that some stones are deliberately made in this way: they are “coated stones”.
In either case, it suffices to vigorously rub the surface of the stones with a rough cloth to reappear the shadows on the refractometer.
Reading cabochons: use of the the refractive index reading for cabochon cut stones is extremely delicate. Indeed, the contact between the stone and the reading table plays a determining role in the use of the refractometer.
Faceted cut stones exhibit flat surfaces, and the reading of their index does not pose a major problem. On the other hand, the rounding of the cabochons creates a difficulty. The “point method” overcomes it.
It is first a question of reducing as much as possible the drop of liquid ensuring the contact optic (either by depositing it using a capillary tube, or by wiping it on the stone to leave only a very small amount).
A good method is to try to read the graduation of the scale while being about thirty centimeters from the eyepiece. After a few trips look, we spot a small darker disc which is precisely placed on the scale at the refractive index of the observed gem.
WHICH LOUPE DO I NEED?
It must be achromatic and aplanatic. We consider as “good” a magnification 10. It is recommended to choose loupes from a field of fairly broad vision. Some of them are equipped with LEDs.
WHAT IS THE BEST MICROSCOPE?
The Best Microscopes are those which have the brightest backlighting, and with variable magnifications.
When choosing a microscope pay attention to the system lighting that we are going to use, to have all the possible choices of illumination incidence. Fiber optics are an elegant solution to these problems.
WHY SHOULD I USE A DICHROSCOPE?
This small, very simple device makes it easy to recognize gems dichroic. It makes appear on the stone two luminous squares, each of color different.
WHAT IS A SPECTROSCOPE?
The spectroscope is essentially a laboratory device. It is used to evaluate the light emitted by the atoms of a stone. This allows the identification of the elements and compounds that are present within the structure of a gem.
In addition, there are small, space-saving models that can be useful for professionals.
Handling spectroscopes requires some practice – and it is necessary to understand the full spectrum of colours, and their association with each element.
Some stones can only be differentiated by using spectroscopy. For example; some Garnets have the same refractive index as ruby and appear anisotropic on a polariscope. Only the spectroscope examination removes this ambiguity.
WHAT DOES THE ULTRAVIOLET LAMP DO?
This lamp which, most often, emits UV rays in waves short or long can be used for many tests. The main – and most useful – concerns ruby and diamonds.
UV is used to test the fluorescence of a stone. UV lamps are also used in CVD detection machines, as natural diamonds and CVD diamonds react differently to absorbing UV lights.
However, this is an additional test which is by no means sufficient for identify a stone.
WHY USING DENSE LIQUIDS?
Immersed in certain liquids, the stones float or fall more or less quickly. This phenomenon makes it possible to measure their density.
Commonly used fluids are:
- bromoform: 2.90
- methylene iodide: 3.33
- Clerici liqueur: 5.00
Two precautions are in order:
- pay attention to the vapors given off by these liquids. They are unpleasant and dangerous.
- be careful not to mix them: they would then lose their specific density. The stones must therefore be thoroughly dried each time a new liquid is used.
WHAT GEM TESTER DOES SMART ARTS JEWELLERY USES TO CHECK CVDs?
The QSPEC GLIS-3000 Gem Tester is one of the best ways to spot diamond in his imitations. Both mounted and unmounted!
The Ultraviolet fluorescence image and the phosphorescence image of natural diamond and synthetic diamond are different. GLIS-3000 excites diamond to becomes luminescence through the built in Ultraviolet light source, captures and records the fluorescence and phosphorescence image of the sample, and we can find out the position of the suspected diamonds with problem by analyzing the relevant images.
WHAT ARTE THE BENEFITS OF A DIAMOND 360 DEGREES PHOTOGRAPHY SYSTEM?
To be able to have a designated online inventory hosted in the cloud became key especially following the Pandemic and the limitations in international travels.
With this state-of-the-art equipment couples with a powerful DSLR and macro lens from Canon, Diamonds can now be seen under their true nature.
You can have a 360-view coupled with views such as Dark-Field, Heart Pattern, Arrow Pattern, AGS ASET® Scope, IDEAL Scope, Fluorescence and Inscriptions (Girdle Cert number…)
Bruno Radegonde – Contributor – I’m a French Business Developer based out of Bangkok since 2010. Smart Arts Jewellery has been my beloved home since 2019 where I handle both Marketing & Sales.
