How to Buy a Colored Gemstone

Ok, maybe the title is a bit brash, since I can’t cover all you need to know about every gemstone in one post. But this will give you some essentials you need to know before you splurge on a colored gemstone piece of jewelry. All the variables mean that a colored stone purchase is pretty complex, and colored gems aren’t always as well-documented as diamonds are.

Here’s what you should look for and ask about when buying a colored gemstone:

Heated or Treated?

Almost every type of colored gemstone has some potential for treatment. Some, such as sapphires, are heated to remove internal inclusions and improve their color. Others, like Emeralds, have materials such as oil or resin filled into fissures within the stone to improve their appearance. For a complete graph of gemstones, their potential treatments and the relative permanence of those treatments, click here.

It is quite rare for gemstones to have no treatment at all, and this will increase the value tremendously, so if a retailer or jeweler tells you that something is untreated, your next statement should be “prove it”! There should be some sort of documentation from an accredited gem lab to show that the gem is untreated (see the next point).

Sapphire and Diamond Ring in Platinum by Mark Patterson, from

Sapphire and Diamond Ring in Platinum by Mark Patterson, from

Show Me the Paperwork!

A gemstone should have some documentation, called a certificate, from an accredited gem lab if it is a larger carat weight (over 2.50 or 3 carats in the case of Sapphires, Rubies or Emeralds), is rare in some way, and ESPECIALLY if untreated/unheated. In general, a lab report for a colored gemstone will document the color, transparency, shape, cut, dimensions, carat weight and a photo of the gem. If you are talking about a major purchase, $10,000 or more, you better have some independent documentation about the gemstone’s specs. Don’t accept a retailer’s word for it: get it in writing and have them explain it to you.

In the recent past, there were several gem labs who did independent analysis on colored gemstones: AGTA’s GTC (American Gem Trade Association’s Gemological Testing Center), GIA (Gemological Institute of America), and Gubelin Gemmological Laboratory. Unfortunately, AGTA closed its Gemological Testing Center on July 29, 2009. This is a big loss for the jewelry industry, as AGTA’s lab was highly regarded for their expertise and integrity. GIA is a respected source for colored gemstone lab reports, which document the color and cut details, plus their origin (if discernible) and treatments (or lack thereof). GIA also has a great colored gemstone tutorial here. Gubelin is a little less familiar to US clients, but sources I checked with said that they trust their lab reports as well. If you purchase a gemstone with paperwork from these labs in particular, you have something concrete you can use to compare value.

22.66 ct Unheated Kashmir Sapphire Sold at Auction for $3.1 Million

22.66 ct Unheated Kashmir Sapphire Sold at Auction for $3.1 Million

The Very Important Final Consideration: I.T.C.S. (It’s the Color, Stupid!)

Much like Bill Clinton’s famous “it’s the economy, stupid!” note on the wall during his 1992 election campaign, it’s important to stay focused on the most critical element: the color. Sure, there is clarity to consider (the relative freedom from inclusions), and how well the gem is faceted. There are also the technical elements of hue (the color), tone (how light or dark the gem is), and saturation (the intensity of the color from weak to vivid) of the color itself.

But there is a more visceral test to conduct with your GUT. Does the color catch your eye from a distance? Does it appear to be lit from within? In the case of a deep blue sapphire, can you get lost in its velvety cobalt depths? Does it glitter, snap, twinkle? Does it make your heart beat faster, make your palms sweat a little? Then you’ve got your gemstone.

8.62 ct Natural Paraiba Tourmaline, AGTA Spectrum Award Winner

8.62 ct Natural Paraiba Tourmaline, AGTA Spectrum Awards

The perfect setting.

Unless you’re a collector buying a loose specimen, you need to consider the setting. Does the setting make a good foil for the gemstone? Does it seem proportioned and pleasing in shape and size? It should enhance the color, such as nice white diamonds providing some contrast to the colored stone. The metal color should also enhance the color of the gem. Yellow gold usually looks good with warm-colored gems like Rubies and Emeralds, while Sapphires can look good with cool white metals (white gold or platinum) OR yellow gold, depending on the design. Sometimes the actual head that holds the colored gem will be a different metal than the metal holding the diamonds or the band of the ring. Pastel-colored gems might look best with white metals, but it depends on the design. Some designers do a great job with interesting combos of different gem and metal colors.

Green Garnet with Tsavorite and Diamond Ring in 18kt White by Gumuchian Fils, $1829 from

Green Garnet with Tsavorite and Diamond Ring in 18kt White by Gumuchian Fils, $1829 from

Bottom Line:

Maybe even more than an engagement ring, a wise gemstone purchase depends on finding a reputable physical jeweler in your area where you can compare and evaluate. This is a very hard thing to buy online or over the phone. You really need to see it. If you need help finding a local jeweler who specializes in colored gemstones, click here to send me a note about what you’re looking for and where you’re located (or leave a comment with your email below). I will do my best to help recommend someone in your area.

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