How to Appraise Gemstones

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Gemstones are appraised by color, cut, clarity and carat.
Gemstones are appraised by color, cut, clarity and carat. (Image: Jeffrey Hamilton/Digital Vision/Getty Images)

Gemstones radiate beauty, intricacy and brilliance. But, determining their true market value requires a skilled appraisal. Gemstones, including diamonds, sapphires, topazes and amethysts, must be appraised (measured) by color, cut, clarity and carats, otherwise known as the four C's. Gemstones that have darker, richer colors, clearly defined and numbered facets, as well as flawless purity, command the highest values, according to the Gemological Institute of America (GIA). With an abundance of imitations and synthetic jewels on the market, it is imperative to know the basic characteristics that distinguish authentic gemstones from lookalikes before investing in or selling them.

Weigh each loose gemstone using an electronic microbalance scale to determine its carat, a gemstone's unit of weight. Then measure each stone with a specialized optical measuring device to determine proportions, symmetry and facet angles, specifically the stone's cut. If the gemstone is mounted or strung in a setting, it can be measured but not weighed.

Grade each gemstone for color using the GIA color scale. A gemstone's overall color value is determined by hue (spectral color), tone (lightness or darkness) and saturation (purity). Each characteristic is graded on a scale of 1 to 10, with 10 being the highest. A dark, rich gemstone, such as the Hope Diamond, for example, would rate high on the GIA color scale for hue, tone and saturation. A flawed, cloudy diamond, on the other hand, would yield a much lower rating.

Evaluate each stone's clarity by the GIA scoring scale respective to its type. Gemstones are categorized into three clarity types and are graded only against other stones in the same type category. For example, a Type I stone, such as topaz would be graded differently from a Type III stone, such as an emerald. Clarity is scored with a VS scale, which ranges from I-3 (poor) to VVS (excellent).

Record the value of each gemstone and keep each record in a safe place. If the gemstone is not yours, ensure that you inspect it to make sure the original stone, along with the value documentation, is placed in its original container. When returning a gemstone to a client, be sure to deliver it either in person or by courier as a high-value item.

Tips & Warnings

  • Keep informed on the latest government provisions, laws and requirements regarding the insurance of gemstones in your charge or possession.
  • Study market trends and price values of gemstones consistently to ensure you always get the best value for your gems and those of your clients.
  • A gemstone's country of origin, if it can be verified, can have a positive effect on the value.
  • When purchasing gemstones, be aware of discount jewelry stores that also offer appraisals. In such cases, the "appraisal" is not much more than a sales gimmick used to inflate the price and for insurance. In other words, sales and appraisals are best conducted as separate businesses.
  • Ask if the gemstone has been treated and to what extent. Gemstones that have been overly treated by heat, dyes, oils and fillings to improve color and clarity are often degraded in value.

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