Sailing the 4Cs: new dangers to avoid when buying diamonds

Holiday season is one of the most popular times for marriage proposals, so there is some serious ring shopping going on. Anyone who has ever shopped for diamonds, whether for an engagement ring or a design of your own, knows there are 4 Cs to look out for: cut, color, clarity, and carat weight.

Once you’ve got those down, you’re solid, right? Bad news: Any one of those Cs can trip you up. And don’t rely on that certificate. Counterfeit reports are on the rise and even reliable ones have their limits.

“The first thing you need to know is what to look out for,” says appraiser and gemologist Antoinette Matlins. “There are ways to alter or conceal each and every one of the 4Cs on which the rarity and value of diamonds are based — and many people in the trade today do not really understand the 4Cs correctly themselves!”

Antoinette Matlins at International Gemmological Conference in London, 2009

Antoinette Matlins giving a demonstration at the International Gemmological Conference in London, 2009

Uh-oh. First lesson: come to this venture armed with knowledge and a good loupe. “From the very start, you need to get at least enough information to have a much more in-depth understanding of the 4Cs, especially as it relates to how each ‘C’ impacts the beauty as well as the cost,” Matlins says. “Then, you need to understand what can be done to alter each of these factors.”

“It has become a market where people think that if they have a ‘diamond grading report’ from a respected lab, that’s all they need to create a successful diamond business. This is absolutely not correct, and if you make this assumption you will suffer costly consequences in every way.”

Let’s break that down into Cs.

From Antoinette Matlin's Diamonds buying guide.

From Antoinette Matlins’ Diamonds Buying Guide.

Color and clarity

Among the many ways flaws can be masked:

• Cracks can be filled with lead glass so they become completely invisible, even with a 10x jewelers loupe  – unless you know how to use it properly to spot this treatment.

• Black inclusions can be lasered out so they can’t be seen.

• A stone can be coated to improve its whiteness or create a more appealing fancy color. “Once you get to a certain size, fancy colored diamonds are likely to have a report from a respected lab,” Matlins says. “If they don’t, think twice – or, better yet, run in the other direction.”

Yellow or brown diamonds under half a carat often don’t have lab reports, yet they sell for more than off-color diamonds. Often these melee diamonds have been coated or “sputtered” on the pavilion (under side) with a fancy yellow or cognac brown that can scratch or chip off over time. Test for it: Scratching with a carbide scriber won’t scratch a diamond but will reveal a surface coating through a loupe.

“They’re out there everywhere,” Matlins warns. “But who would bother to send 4-point melees to the labs? Nobody. So, fancy colored diamonds are an area of concern.”

Diamonds: Antoinette Matlins Buying Guide

Click image to find book on Amazon.

Differences in cutting can have a dramatic impact on value. “Two round diamonds of the same size, color and clarity can have a cost spread of more than 40 percent based on differences in the cutting alone,” Matlins says.


If that’s not bad enough, it seems counterfeit lab reports are on the rise. Matlins reports the GIA recently encountered yet another incident of this. Someone bought a diamond accompanied by a counterfeit report. “Even stones accompanied by legitimate reports may have been damaged, re-cut or re-polished after the report was done, altering the grade,” she says.

Look for dates. If a report was made 10 years ago, check the diamond carefully for wear or damage. “If a diamond hasn’t been resubmitted for a new report in several years, there could be a reason,” Matlins says.

Check for reputable labs. For an undercover story that aired on ABC in July, Matlins posed as a mother shopping with her son for an engagement ring on 47th Street, Manhattan’s famed diamond district. “A number of stones we looked at had reports from labs you’ve never heard of,” she says. “They look like official documents and I’m sure they have a legimate office and a professional-looking website, except there is no such professional lab at that address. The whole operation is counterfeit, if you will.”

Even with a legitimate lab, there is often inconsistency. “Stones with borderline colors or clarity grades often get the higher grade, and you over pay,” Matlins says.

Labs she gives the stamp of approval in her diamond buying guide:

Screen Shot 2013-11-15 at 1.47.15 PM

Assuming the information on a report is reliable, every grade covers a range – and that can complicate valuation. “You might have a diamond that doesn’t have as many or as big or visible flaws but there might be a larger fracture that reaches the surface on top of the stone,” Matlins says. “It’s nothing you see or that poses a risk but the report grade is worse. Well, actually that stone may be a much better purchase than the one with the better grade.”

“The 4 Cs on the surface are very clear, but there is so much to understand about what goes into those grades,” she says. “No professionally-trained person in the diamond field with any experience would ever buy a diamond based on a report without looking at the stone and valuating it themselves.”

How to avoid the pitfalls of diamond-buying?

Read up. I recommend two of Atoinette’s many excellent guides for this mission: Diamonds: Antoinette Matlin’s Buying Guide, 3rd edition and Gem Identification Made Easy, 5th edition. The diamond book covers everything you need to know about the points Matlins made here, except for teaching you how to actually do the grading. The gem identification book explains, in layman’s terms, the instruments you need, how to use them properly, and what they will reveal re: treatments, fillers, synthetic vs. natural.

Buy the right loupe. Matlins advises buying a good 10x loupe. For diamonds, she recommends using a specially modified dark-field loupe, a UV lamp with both long-wave and short-wave output, and a diamond “type” spotter. “These alone will save you from costly mistakes once you know how to use them and gain some experience, comparing stones side-by-side,” she says. You can buy one of her handpicked dark-field loupes at GemStone Press for $59.

Take a course. Ideally, she says, you should also take at least a short course in diamond grading. If that sounds like overkill – well, it may be if you’re on a one-time mission for a modest engagement ring, but if you’re serious about this and think you may be in the market for more diamonds in the future, a basic course is not a bad idea.

Get an expert’s opinion. Barring that, a significant diamond purchase is worth running past a skilled and objective expert. Matlins advises against settling for the neighborhood jeweler on this. “Find a knowledgeable, experienced gemologist who works with diamonds,” she stresses. “Many jewelers are merchants who know only what the seller told them. What you need is someone up to date on synthetic diamonds and treatments, as well as being proficient in diamond grading, to confirm your purchases, ideally before you buy.”

If you also want input on whether or not you over-paid, you need a gemologist-appraiser, Matlins says, “someone who is both a gemologist with respected credentials and lots of diamond experience and who can value what you have because they are in the wholesale marketplace and know the cost of comparable stones.”

Members of the Accredited Gemologists Association or someone with the Master Gemologist Appraiser credential from the American Society of Appraisers will have the credentials and experience you’ll need.

You can contact Antoinette or read more about all this on her website.

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1 comment for “Sailing the 4Cs: new dangers to avoid when buying diamonds

  1. August 25, 2017 at 12:12 am

    Excellent post with very pertinent and useful information not only for the people who are interested in buying diamond jewelry but also for everyone in the jewelry business. Thank you for sharing.

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