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The Gemstone Blog

Gem Identification - The Polariscope

Posted by MICHAEL Hart on

Gem Identification - The Polariscope

The Polariscope is a fairly simple instrument that can help to determine whether a gem is singly refractive (SR) or doubly refractive (DR). Polariscope testing takes advantage of the way that Gemstones and polarized light interact.  The first thing to know about the Polariscope is that it only analyses transmitted light, so a gem must be transparent to translucent for polariscope testing to be successful. A Polariscope is made up of a light source and two polarizing filters. The polarizing filters are plastic discs that are designed to transmit polarized light. The filter on the top of the device is called...

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Gem Identification - How to Test a Gem's Refractive Index (RI)

Posted by MICHAEL Hart on

Gem Identification - How to Test a Gem's Refractive Index (RI)

Of all the tests used in gem identification, measuring refractive index is one of the most effective ways to tell one stone from another. When a beam of light strikes a gem, it slows down and sometimes bends. This is known as refraction. Each gem has a different refractive index that can be determined using a refractometer. The amount of refraction depends on the gems optical density and the angle at which light strikes its surface. Each gem has its own chemical composition that produces a specific RI reading. Some gems that are doubly refractive have two RIs. When light...

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How to assess a mounted diamond

Posted by MICHAEL Hart on

How to assess a mounted diamond

Retail jewellers rarely deal in loose stones so it is important for people who work in retail (as well as informed customers) to be able to estimate the proportions of diamonds that are mounted in jewellery. This post reviews some of the key formulas professionals use to assess the proportions of mounted diamonds.  Evaluating Clarity This first thing to understand about mounted diamonds is that the mounting can hide inclusions. Mountings such as prongs can also interfere with lighting and cause reflections that can be misleading. To see what’s under a prong, find the prong’s reflection on the opposite side...

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How Fancy Cut Diamonds are Graded

Posted by MICHAEL Hart on

How Fancy Cut Diamonds are Graded

The Round Brilliant is by far the most popular diamond cut on the market. But with so much focus on the round Brilliant, it’s easy to forget about the wide variety Fancy cuts that are available. This post introduces the reader to the world of Fancy Cut Diamonds and how industry professionals grade them.  There are three major cutting styles that most diamonds fit into: Brilliant Cut, Step Cut and Mixed Cut. Many Fancy cut Diamonds are variations of the Round Brilliant. Oval Cuts, Marquise, Hearts, Pears, Trillions and Cushions evolved from the round Brilliant. All Fancy Cut Diamonds have...

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Estimating Diamond Proportions (Part 2)

Posted by MICHAEL Hart on

Estimating Diamond Proportions (Part 2)

In recent years, the cut of a diamond has become an important component that consumers consider. There are set ranges of proportions that are favourable and diamonds outside these ranges will receive a lower cut grade. This post is Part 2 of how to estimate a diamonds proportions. It reviews how to estimate the pavilion, cullet and finish of a diamond. The Pavilion The Pavilion is an important part of the diamond. It breaks white light into spectral colours and creates the fire we see in diamonds. There are two ways that diamond professionals describe the pavilion: Pavilion Depth Percentage...

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