How do we know the difference between a diamond and cubic zirconia, or if a blue stone is paste or sapphire and then, if its natural, colour-enhanced, synthetic, treated, or damaged?

Gemology involves studying the physical and optical properties that make gems unique. The identification process involves analysing these properties to help us grade stones, determine natural stones from synthetics and differentiate one species from another.

Here are 10 gemmology tools we use at Leonard Joel to distinguish or measure these properties.

10x Triplet Jeweller’s Loupe

This is used for all initial inspections. It allows us to closely inspect the jewellery and make instant assessments, based on the internal and external features of the stone. Sometimes this means a diagnosis of a stone simply from the inclusions.

Binocular Microscope

A binocular microscope offers higher magnification of jewellery and gemstones and can be extremely useful in the identification of difficult gemstones such as synthetics. The gemmological microscope also has light sources, which assist in illuminating the gems and offer the ability to see more inclusions in greater detail under higher magnification.

Refractometer

This is one of the most important tools in the gemmologist’s tool kit. The refractometer can give you the refractive index (sometimes diagnositic) including the optic character and sign of the gemstone.

Polariscope

The polariscope is also a critical piece of equipment, allowing us to easily identify single and double refractive gemstones and assist us in quickly differentiating stones, for example, a garnet from rubies. It can also help to distinguish between natural and synthetic materials.

Dichroscope

The dichroscope allows us to see the pleochroism in a gemstone (the multiple colours that many gemstones produce). Our eyes cannot separate these colours in most cases, so the dichroscope uses calcite crystals to separate the light waves, which allows us to see the individual colours. This can also assist in the identification process of a gem.

Chelsea Filter

The Chelsea filter can help separate imitations from the real thing. It can identify the chromium content of Colombian emeralds, give a red reaction to natural lapis lazuli, show chromium content of jade, separate synthetic blue spinel from natural.

Electronic Scales

Traditionally, the weight of a gemstone is expressed in carats (1 carat = 0.20 grams or 200 milligrams). For gemstones weighing less than 1 carat, their weight is expressed in units that are 100 times smaller, known as points (e.g. 50 points = 0.5 carats). Scales are used in determining the pricing of gold jewellery and size of loose stones.

Ultraviolet Cabinet and Long Wave/Short Wave UV Light

Both longwave and shortwave ultraviolet light (UV) is used in the identification process. The luminescence of a stone can help us differentiate between certain natural and synthetic gems.

Ultravoilet testing can expose enhanced layers of diffusion-treated gems, oils used as fillers in emeralds and other gems, and components in assembled stones which often have different fluorescent qualities to the rest of the specimen material. Seeing this at an early stage of your examination can save time later.

Leveridge Gauge

Gauges are vital in making weight estimations of set stones and measuring loose stones. In many cases, the stone size is the only key to weight estimation, which can be carried out with measurement formulas.

Master Colour Grading Set

This master set helps us assign a colour grade to diamonds. The scale begins with the letter D, representing colourless, and continues with increasing presence of colour to the letter Z. Each letter grade has a clearly defined range of colour appearance. Diamonds are colour-graded by comparing them to our stones of known colour under controlled lighting.

JULIE FOSTER
Head of Jewellery