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It's reasonable to expect lasting value and enjoyment when you purchase colored gemstone jewelry. Learning a few things about gemstone quality and value will help you make sure you get what you want – and deserve.

You can start by trusting your instincts. Sensory appeal is always paramount. So, if a particular gemstone or jewelry design "speaks" to you, by all means listen!

You can also use what you know about the 4Cs. The familiar diamond value factors of color, cut, clarity, and carat weight apply to colored gems as well. However, each gem variety is judged by its own potential: no one expects an aquamarine to have the same color as a sapphire or an emerald to be as flawless as an aquamarine. But there are a few general rules you can use to judge gemstone quality.

The 4Cs
Gemstone Information Manual (American Gem Trade Association Information Manual)

The Four C's (excerpt from AGTA)

Color
Some gemstones come in a multitude of colors, while others have more restricted palettes. Experts analyze all these chromatic options in terms of three essential components: hue, tone, and saturation. Hue is the basic color sensation – blue, red, green, and so forth, plus blends like purplish red and violet-blue. Tone is a color’s lightness or darkness, and saturation is its visual intensity.

Gemstone Hue Chart

Colors of pure hue, medium tone, and high saturation are generally most valuable, but different kinds of gems have differing potentials in this regard. For example, sapphire and tanzanite can reach a deeper blue than aquamarine, topaz, or zircon. Color ranges can overlap to some extent, so different gemstones may have the same color. Each is valued according to its own unique possibilities, however. Thus, the particular tint that's considered "best" for one gemstone might be "medium" for another.

Gemstone Saturation Chart

Gemstone Tone Chart

In buying decisions you need to be aware of color ranges and objective value assessments, but it’s best to rely on your eyes and heart. Pure or mixed, light or dark, vivid or muted – whichever color holds the most appeal for you is the one to choose.

Kashmir Sapphire Example

 

Cut
Choices in cut are almost as varied as for color – and they're every bit as intriguing. Transparent colored gemstones are most often faceted like diamonds, in dozens of geometric shapes and styles. The ancient domed form known as the cabochon is traditional for gemstones like jade, opal and turquoise. It helps to bring out the special optical effects seen in star gems and cat’s-eyes, too. Today many kinds of gemstones are fashioned into carvings. These range from classic cameos and natural motifs to designs that push the edge of abstract expression.

Whatever the technique may be, cut is chiefly responsible for revealing a gemstone's beauty. Its contribution to appeal and value arises from the cutter’s artistic creativity, technical skill and patient labor.

To judge the quality of cut, examine the gemstone as you hold it at arm's length and rock it gently back and forth. The overall form ought to be pleasing and dynamically balanced. Color and light should dance throughout a faceted gemstone, with no washed out "window" in the center or dead spots around the edges. When you look close-up, details like facet shape need to be precise, with polished surfaces appearing smooth and bright.

Typical Cut Shapes for Gemstones

Clarity
Most kinds of colored gemstones may have internal characteristics – or inclusions – that it's possible to see without magnification. Many of these are simply byproducts of the natural processes that create gemstones within the Earth. Among the most common are tiny mineral crystals that became caught up in larger gemstone crystals as they grew. As long as such inclusions aren't prominent, they don’t diminish a colored gemstone’s beauty or desirability, and have little effect on its value.

There are some exceptions to this rule, however. You can expect a few gemstones to be "eye clean," with only microscopic clarity features. This list includes aquamarine, citrine, tanzanite, and topaz. On the other hand, inclusions in emerald and red tourmaline may be fairly obvious, but won't have a major impact unless they’re also unsightly.

It's important to recognize that inclusions have a positive side, too. They can prove that the gemstones in which they occur are natural – not synthetic or imitation.  Scientists study inclusions to learn the secrets of how gemstones form, and when viewed under a microscope, some are strikingly beautiful in their own right.

Silk. Needly, cloudlike inclusions, known as silk, are visible under magnification, proof of the absence of heat treatment. (Photo: Wimon Manorotkul)

Carat Weight
Like diamonds, most colored gemstones are weighed and priced by the carat. (One carat equals 1/5 gram.) As with color, however, different kinds of gemstones have differing weight potentials.  A few rarely exceed 5 carats in high quality. Many are readily available up to 15 or 20 carats and some can be even larger.

For gemstones with limited weight ranges, per-carat prices usually climb steeply as the carat weight goes up. For those with wider ranges, any increases tend to be more gradual. A 3-carat ruby might have a per-carat price that’s three times higher than a 1-carat ruby of the same quality. As a result, the larger gemstone would cost nine times more than the smaller one. In contrast, a 5-carat amethyst is likely to have about the same per-carat price as a 1-carat amethyst, so it will cost only five times as much.

Besides reflecting the natural rarity of larger gemstones, per-carat price can serve as an indication of other value factors. If two gemstones of the same kind and weight have significantly different per-carat prices, there will be differences in color, cut, or clarity, which you need to consider in a purchase decision.

Gemstone Treatments - Things you should know!
Many of the supplied gemstones on the world market available today have undergone various treatments to achieve a better clarity and uniform colour. The treatment and disclosure is a sore subject for many in the industry as there is still much debate over what is considered acceptible and safe. We pride ourselves for full disclosure and provide refund or replacement guarantees from our own stock and sourced material.

Diffusion Treatment
This particular treatment alters the surface hue of a stone under high heat and various chemicals controlled within a furnace. The colour change is only impregnated in the shallow surface of the gemstone leaving the original undesirable colour in the center. If the stone ever wears, cracks or chips the original colour will be seen and any means of polishing or recutting will result in loss of the colour the stone may have been originally purchased for. This treatment has been noted in varieties of Ruby, Topaz and Sapphire. Reputable dealers will always disclose any such treatment of a stone and many will never deal in this particular treatment due to the lack of longevity the stone will provide for its customer. However this is also a common treatment in Star Sapphire which in turn provides a more prominant star appearing in the stone and is usually sold as Diffused Star Sapphire.

Beryllium Treatment ('Be' is the symbol for the element Beryllium)
This treatment is sometimes known as lattice diffusion treatment but don't be fooled by the many names dealers have tried to cover up this treatment. Essentially Beryllium is an element commonly known to the gem world as it is a component of many gemstones like, Emerald, Beryl and Aquamarine. However this form of heat treatment introduces the element during the heating process to change the colour of the natural stone, it reduces the blue tone producing bright yellows and oranges (padparadschas) which are a sought after variety in sapphire that are naturally very rare, highly prized and valuable. The resulting treated stones are dramatically reduced in value as it is no longer considered of in the natural context. It is very important that this type of treatment is disclosed.

Heat Treatment
This type of treatment is more commonly accepted among the gem world as it is merely seen a continuation of the process with which earth had provided these gemstones to begin with. It is a centuries old artform that is still a tightly kept secret to those in the trade, each different region and variety are all treated differently depending on their makeup from their locale. The end process from treating a stone in this way usually results in a tonal change and clarity improvement as the internal structure is reformed. The detection of such treatments is not impossible as natural inclusions of gas bubbles and rutile leave feint traces which a gemologist can easily discover with a microscope.

Amethyst – lightens the color and will change the color of pale amethyst to yellow that will usually be sold as citrine.
Aquamarine – removes the greenish undertones that are common in this stone to produce a more blue stone. Also deepens the color
Kunzite – to improve color
Morganite – heat treatment changes the color from orange to pinkish
Ruby – heat treatment can improve colors. Will also remove iron stains, dissolve inclusions and fill tiny cracks
Sapphire – to lighten or intensify color and to improve the uniformity of the color
Tanzanite – to produce a more desirable blue shade
Topaz – when used with irradiation, heat treatment will produce shades of blue. Also done to produce a pink topaz
Tourmaline – to lighten darker shades of tourmaline. This is usually done with the green and blue varities
Zircon – to produce red, blue, or colorless stone

Fractured Filled Treatment
Natural gemstones are far from perfect and usually contain many imperfections called inclusions. Theres a variety methods used to fill in the tiny cracks and voids, aswell as a vast range of chemicals used like oil, wax, glass, epoxy and borax. The filling of these cracks and fractures helps to eliminate dead spots where the light will not travel through the stone. Emerald is a commonly oiled gemstone as it appears naturally very fractured. However more recently rubies have been found to lead glass filled as it has similar optical properties which make it a great combination for improving the stones colour and clarity. These stones represent an excellent value in the market, so long as the treatment is disclosed and the price is appropriate

Irradiation Treatment
Although the irradiation of gemstones can leave some residual radioactivity, its duration is relatively short. Government agencies in the USA, and other gem irradiating nations, have strict regulations for the holding and testing of irradiated gems to assure that they are not released to the public until they are safe to handle and wear. Alot of the Topaz on the market has undergone treatment to improve their colour for sale. There does exist natural coloured varieties of Topaz although these are rare and usually pale in colour, the price difference is also reflected in the quality of the stone.