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How to tell if a diamond is real

how to tell if a diamond is real - image of ring

This diamond ring demonstrates the gray reflections that indicates it's genuine.

How to tell if a diamond is real

By Mary Van Doren on November 01, 2017

Manmade diamonds and great fakes make it hard to know how to tell if a diamond is real 

Getting engaged? Thinking of buying a piece of diamond jewelry from someone who’s not an established, reputable jeweler? Maybe you inherited some jewelry you know nothing about. Now you want to know how to tell if a diamond is real. 

You can buy a diamond that has a certificate from a respected independent gem lab, such as the Gemological Institute of America (G.I.A.), International Gemological Institute (I.G.I.), Gemological Science International (G.S.I)  or American Gem Society (AGS). 

The certification proves the stone is natural and documents the color, carat and quality of the diamond.  

Some people prefer to buy in the after-market, such as pawnshops or on Craigslist, where even a real diamond may not have a certificate. In that case, here are some tips on how to tell if a diamond is real. 

How to tell if a diamond is real: Simple home tests 

As noted by Guru_Guy, an experienced researcher and verified Expert on JustAnswer, determining whether a diamond is real can often be difficult. “There are a lot of high quality fake diamonds out there and it often takes a professional to make a conclusive determination.” 

But if you want to give it a shot yourself, try these tests. Some of them can be used on mounted diamonds, others only on unmounted stones. 

Tests for mounted stones: 

  • The scratch test: This is an old standard but can be misleading. Yes, real diamonds will scratch glass, but so do a lot of fakes, including some high-quality cubic zirconia.  
  • The fog test: Make sure the diamond is perfectly clean and breathe on it like you would to fog a mirror. If it stays fogged for 2-4 seconds, it’s fake. A real diamond disperses the heat right away so by the time you look at it, it has already cleared up.  
  • The UV test: Most – but not all – diamonds will show fluorescent medium to strong blue when put under an ultraviolet light (not the same as a black light used with posters!), while 99% of all fakes don’t. 
  • The reflections test:  A real diamond's reflections usually show up in various shades of gray. When looking straight down through the top of the diamond, rainbow reflections will indicate either a very low-quality diamond or a fake. 
  • The sparkle test: Look for brilliance and intensity of sparkle from the stone. Cubic zirconia usually exhibits a greater spectrum of color than real diamonds when light is focused on the stone. Moissanite, an almost identical twin of diamond in its sparkle, will also display a rainbow. 

Tests for unmounted stones: 

  • The transparency test: Put the diamond upside down over some newsprint. If you can clearly read through the stone, or even see blurred smudges, it’s not a diamond, because a diamond refracts light too sharply for the text to be readable. Unfortunately, even this isn’t foolproof, because you can read through a diamond if it’s cut disproportionately. 
  • The dot test:  Draw a small dot with a pen on a piece of white paper and place the stone over the center of the dot. Look directly down on it. You won't be able to see the dot through a real diamond. Otherwise, you’ll see at least a circular reflection in the stone.  
  • The heat test: Heat up the stone with a lighter for 30 seconds, then drop it into a glass of cold water. The rapid expansion and contraction will overwhelm the tensile strength of weaker materials like glass or quartz, causing the stone to shatter from the inside. This will have no effect on a real diamond. 
  • The water test: Drop an unmounted stone in a glass of water. Due to its high density, a real diamond will sink to the bottom. Fakes will float midway or on the surface.  

How to tell if a diamond is real: Using jeweler's tools

You can always buy professional tools to use at home, especially if you plan to test multiple diamonds. 

 Try these: 

  • Carat or gram scale: Use this to weigh the diamond. Cubic zirconia, the most common of fakes, weighs roughly 55% more than diamonds for the same shape and dimension.  
  • Electronic diamond tester: These measure how fast a stone conducts heat, which is different for every gem. Cheap ones (in the $12 range) are readily available, but can give false positives if the stone is mounted. Professional testers cost around $200-300, and some can distinguish between diamonds and its near-twin moissanite. 
  • Jeweler’s loupe: Use this magnification tool (inexpensive at $12 or more reliable at $80-$95) to view the stone from the top and look for ...
      1. How well the facets (cuts on top of the diamond) are joined. They should be sharp, not rolled.
      2. The girdle (the widest part of the diamond when viewed from the side) to see if it’s faceted or frosty for a diamond, or waxy and slick for a fake.
      3. Any flaws such as carbon, pinpoints, small cracks, which are nearly impossible to put into a fake.
      4. NOTE: Synthetic, lab-grown diamonds, while much less valuable, are genuine diamonds and will show no imperfections.  There are complex tests to identify synthetic diamonds, but they’re almost identical to mined diamonds. 

How to tell if a diamond is real: A professional appraisal

Deborah, another Expert on JustAnswer, points out that the quickest and most reliable method to establish authenticity is an independent diamond appraisal. She suggests that you do some research to find the best appraiser. The fee should be in the range of $35-$75.  

You should also ask if your jewelry or stone would always be in your presence.  

“If the appraiser says they will not evaluate the jewelry, in front of you, find another appraiser,” she advises. 

Here are some of the tests an appraiser may perform:  

  • The heat probe test: The tight, even crystal structure of diamonds makes them disperse heat quickly, so real diamonds won’t heat up easily. Heat probe tests take about 30 seconds and are often done free of charge. They also don’t hurt the stone the way some other testing methods can. 
  • The microscopic examination: An appraiser will place the diamond under a microscope with the top facet face down and gently rock the diamond back and forth. If a slight orange flash along the facets is visible, the stone may actually be cubic zirconia, or cubic zirconia was used to fill imperfections within the diamond. 
  • The X-ray examination: Diamonds have a radiolucent molecular structure, which means don't appear in X-ray images. Glass, cubic zirconium and crystals all have slightly radiopaque qualities that make them show up clearly on an X-ray. 

All in all, it’s usually worth spending some time and money on identifying a diamond, especially if you want to insure it for it’s true value. And if you have any additional questions about how to tell if a diamond is real, you can get a fast, convenient answer from the Experts on JustAnswer. 

Have you ever discovered a fake diamond that you originally thought was real? Please share your experiences with us in the comments below!