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It's all about colour!

Colour should be the first thing you think about when shopping for gemstones.  There are several methods of describing gemstone colour, but they all essentially describe the same properties:  hue, tone and saturation.

Hue describes the primary colour of a stone and any other visible hues which modify the primary hue.  A "red" stone isn't just a red stone.  It can be purplish-red or orangish-red or a host of combinations in between.

Tone refers to the lightness or darkness of the hue and is generally expressed as very light, light, medium-light, medium, medium-dark or dark.

Saturation describes how much of the primary hue a stone contains.  Stones described as having strong or vivid saturation have very little brown or gray interfering with the primary hue and generally are considered the most desirable.

Clarity

Most gemstones are colourless in their purest form. However, most of the time, the gemstone's crystal will contain impurities which cause it to have colour, and it most likely will have some type of inclusions as well.  Some gemstone varieties are by their nature more included than others. It is rare for a coloured stone not to have inclusions, and, in some cases, inclusions are desirable, such as the horsetail inclusion which is often present in demantoid garnet of Russian origin. For this reason, coloured stone clarity is not described in the same way as diamond clarity.

For instructional purposes, the Gemological Institute of America (GIA) divides coloured gemstones into three types based on the amount of inclusions usually present in them. While the terminology is the same, a Type 3 eye clean gemstone will have more inclusions than a Type 1 eye clean stone, as described in the charts below.

 

GIA Coloured Stone Clarity Grading Charts for Type 1, 2 and 3 Gemstones

 

GIA Type 1 Clarity Chart

Type 1 gemstones are usually "eye clean." Gemstones in this category include Aquamarine, Chrysoberyl (Yellow and Green), Heliodore, Morganite, Quartz (Smoky), Spodumene, all Tanzanite, Tourmaline (Green) and Zircon (Blue)and Diamond.
Eye Clean - Eye clean to the unaided eye.
Slightly Included - Minute inclusions, difficult to see with the unaided eye.
Moderately Included - Minor inclusions, somewhat easy to see with the unaided eye.
Heavily Included - Prominent inclusions, negative effect on appearance and/or durability.
Severely Included - Prominent inclusions, severe effect on appearance and/or durability.
 
 

GIA Type 2 Clarity Chart

Type 2 gemstones are usually included. Among them are Andalusite, Alexandrite, all Garnet, Iolite, Peridot, Quartz (Amethyst, Citrine, Ametrine), Ruby, Sapphire, Spinel, Tourmaline (all but Green, Red and Watermelon) and Zircon (all but Blue.)
Eye Clean - Eye clean to the unaided eye
Slightly Included - Minor inclusions, somewhat easy to see with the unaided eye.
Moderately Included - Noticeable inclusions, apparent to the unaided eye.
Heavily Included -Prominent inclusions, negative effect on appearance and/or durability.
Severely Included - Prominent inclusions, severe effect on appearance and/or durability.
 

GIA Type 3 Clarity Chart

Type 3 gemstones by their nature have many natural inclusions. Emerald, Red Beryl and Red (Rubelite) and Watermelon Tourmaline fall into this category.
Eye Clean - Eye clean to the unaided eye.
Slightly Included - Noticeable inclusions, apparent to the unaided eye.
Moderately Included - Obvious inclusions, apparent to the unaided eye.
Heavily Included - Prominent inclusions, negative effect on appearance and/or durability.
Severely Included - Prominent inclusions, severe effect on appearance and/or durability.
 

 

Shape and Cut
The terms shape and cut are not interchangeable.  Shape refers to a gemstone's overall outline.  It can be round, square, oval, pear, rectangular octagonal, triangular or trilliant, to name a few.  Cut refers to the number and arrangement of the facets.  Each shape can be cut many different ways.  Some popular cuts are known as brilliant (for diamonds), Portuguese, step, radiant and mixed but there are many, many more.  There are a few terms, however, that describe a shape and a cut, such as emerald cut or princess cut.  There are also patented cuts, such as the Royal Asscher, which is a square variation of the emerald cut.

A bad cut can ruin a beautiful gemstone. Most coloured stones on the retail market are native cut or cut in commercial cutting houses. Native cut stones are cut in the country of origin by cutters using native style equipment. The stones are often "windowed" or are cut for maximum weight, which saves money, but doesn't always do justice to the stone. Commercially cut stones are generally cut to calibrated sizes and can vary in quality and consistency.

Custom cut stones can take many forms and are limited only by the imagination of the cutter.  The cost of a custom cut stone can be several times of the same native cut stone, but there really is no comparison and the custom cut is worth the extra cost.


An Introduction to Gemstone Treatments

Gemstones have been valued throughout the ages for their beauty and rarity. Advancements in mining technology, as well as global marketing, have created more demand for coloured stones, and a variety of enhancement processes have been developed which ultimately have made gemstones available to many who would never be able to own them otherwise.

Several methods of gemstone enhancement are common in the market today, and, with proper disclosure, are generally accepted within the trade because they have been demonstrated to be stable and permanent. Untreated stones are available, but the vast majority of commercially sold gemstones have been treated by one or more methods.

Very few gem species have not been successfully treated to enhance colour or clarity, and new techniques for enhancing coloured gemstones are continually being developed. These may be difficult, or in rare cases, impossible to detect, even for the most sophisticated laboratory.

The Federal Trade Commission Guides for the Jewelry, Precious Metal, and Pewter Industries states that it is unfair or deceptive to fail to disclose that a gemstone has been treated if:

    (a) the treatment is not permanent.
    (b) the treatment creates special care requirements for the gemstone.
    (c) the treatment has a significant effect on the stone’s value.

The disclosure requirements apply to every level of the trade. Consumers must be presented with disclosure information in plain language at the point of sale.

Here is a description of the most commonly used gemstone enhancements:

Bleaching

The use of heat, light and/or other agents to lighten or remove a gemstone’s colour. This is sometimes used in pearl processing. The bleaching is permanent and stable, but pearls by their nature require special care.

Coating

The use of such surface enhancements as lacquering, enameling, inking, foiling or sputtering of films to improve appearance, provide colour or add other special effects. All "mystic" type topaz is coated and requires special care because the coating may easily be scratched.

Dyeing

The introduction of colouring matter into a gemstone to give it new colour, intensify present colour or improve colour uniformity. This is used in many materials, including jade, chalcedony, agate, pearl and lapis lazuli. Certain dyed materials may fade in light or heat, and extra special care should be taken to avoid chemicals, cosmetics and ultrasonic cleaning.

Diffusion

The use of chemicals in conjunction with high temperature to produce artificial colour change and/or asterism-producing inclusions. It is a violation of the FTC Guides to fail to disclose diffusion on gemstones in advertising, promotional literature or commercial documents. Ruby and sapphire are commonly diffusion treated to improve or change colour and to produce a "star."

Filling

The filling of surface-breaking cavities or fissures with colourless glass, plastic, solidified borax or similar substances. This process may improve durability, appearance and/or add weight. This process has become widespread in the market, particularly in ruby and sapphire.

Heat Treatment

The use of low heat only to effect desired alteration of colour, clarity and/or phenomena. The application of heat to enhance the colour and/or clarity of gemstones has been a common practice around the globe for centuries. This treatment method, which adds no colouring agents or fillers to the stone, is part of the standard polishing and finishing process for many coloured gemstones and is accepted by the jewellery industry and the American Gem Trade Association. The enhanced colour and/or clarity of heat-treated gemstones is permanent. This also may be referred to as "heat only," "low heat" or "gentle heat."

Heating and Pressure

The use of heat and pressure combined to effect desired alterations of colour, clarity and/or phenomena.  Generally used on diamonds, HPHT treatment is difficult to detect without sophisticated laboratory equipment.

Impregnation

The impregnation of a porous gemstone with a colourless agent (usually plastic) to improve durability and appearance. Turquoise commonly is impregnated. The treatment is considered permanent but does require special care.

Irradiation

The use of neutrons, gamma rays or beta particles (high energy electrons) to alter a gemstone’s colour. The irradiation may be followed by a heating process. Stability of the treatment varies based on the type of material. Topaz, morganite and spodumene are commonly irradiated to enhance colour but may fade if exposed to light or heat.

Lasering

The use of a laser and chemicals to reach and alter inclusions in gemstones, usually diamonds.

Waxing/Oiling

The impregnation of a colourless wax, paraffin or oil in porous opaque or translucent gemstones to improve appearance. Emeralds are always oiled to improve clarity and should not be cleaned with harsh chemicals or ultrasonic cleaners.

For more complete information on coloured gemstone enhancements, see the American Gem Trade Association's Gemstone Information Manual.

Synthetics and Simulants

Usually the first question a consumer will ask when considering an item for purchase is, "Is it real," when the question should be, "Is it natural?"  By definition, a synthetic gemstone has the same chemical, physical and optical properties as its natural counterpart but is created in a lab.  So, for example, synthetic ruby is "real" ruby, but it should never be represented as "natural." Synthetic stones may also be referred to as laboratory grown or laboratory created. Because they are created under controlled conditions, synthetic stones don't have the same inclusions as gems formed by nature in the earth, which is why some people think they look "too perfect."  However, because they crystallize in a different way in the lab than in nature, they do have characteristics which a trained gemmologist can generally spot quite quickly under proper magnification.  Sometimes lab created stones are given a treatment that causes internal characteristics that mimic natural inclusions, which can make identification a little trickier. Synthetic gemstones regularly seen in the jewellery market include alexandrite, sapphire, ruby, spinel, emerald, aquamarine, amethyst and opal, among others.

A simulant (or imitation) can be any material, natural or synthetic, which is intended to simulate another material.  The most familiar diamond simulant, cubic zirconia, has no naturally occurring counterpart.  An increasingly popular diamond simulant, synthetic moissanite, does have a natural counterpart, but it is so exceedingly rare that all the moissanite on the market is synthetic.

Synthetics and simulants can offer the consumer the look of natural gems at a fraction of the price, and certainly have their place in today's market, as long as they are accurately represented as such.

-By Cynthia B. Reuschel


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