If you are browsing gems or jewelry for sale and want to quickly determine whether a clear stone is a diamond, there are a few easy tests you can apply without any special equipment. The popular test of scratching the stone across glass or metal isn't very reliable, and might just give you a damaged gem; instead, looking at the way the stone reflects light or if it fogs up when breathed on can give you a better indication of whether or not it's a real diamond. These tests rule out recognizable imposters because they rely on the way a real diamond refracts light, conducts heat, and looks up-close. The only people who can authenticate a stone are certified gemologists specializing in jewelry, however; their services are available for a fee.
The Print Test
If the gem in question is loose and unmounted, try placing it over printing. Diamonds refract so much light that they will not work as magnifying glasses and you would see no lines, circles, or letters through them. Other clear stones like glass or crystal will reveal the print clearly. Be careful: Depending on how a diamond is cut, the print test is not completely reliable.
The Light Test
A similar test uses a small light, such as one that can be carried on a key ring. If you shine the light through the stone and see only a bright halo around the rim, it is more likely to be a true diamond. Looking at the shadows cast by a stone can also help determine what kind of gem it is, as real diamonds typically cast grayish shadows, not rainbows.
The Breath Test
Diamonds are also very good at conducting heat. Breathe on the surface of the stone and immediately check to see if it has fogged up. Quartz, glass, and cubic zirconium will stay hazy for a moment before the condensation dissipates, but you shouldn't be able to see any moisture on a real diamond. One rock, called moissanite, will also pass this test, so it is not completely reliable. If you aren't sure about the stone, you may need to get a complete thermal conductivity evaluation performed by a jeweler.
Look Up Close
Looking closely at the specks, ridges, and facets can give you a clue into the identity of your gem. Diamonds do have inclusions, which are tiny bits of other minerals that were crushed into the stone while it formed, so impurities don't mean a gem isn't real. If the facets have worn or rounded edges, or if the stone looks rippled, bubbly, or pitted, it is probably glass. Gems that are perfectly clear, with absolutely no inclusions, may be quartz.
Tests that Require Tools
If you have some additional tools at your disposal, there are more advanced tests you can use to assess a stone offered for sale. An instrument known as a diamond/moissanite tester evaluates the thermal and electrical conductivity of a stone to determine if it is genuine or a simulant material. Using a scale, you can also compare the weight of a stone to a real diamond for reference; if the weights are different, this is an indicator that the stone is fake. Viewing a diamond under ultraviolet light usually reveals a flash of blue, although very high quality stones don't always do this, so the absence of this color change doesn't necessarily mean a stone is fake.
Certificate of Authenticity
A seller may also have a certificate of authenticity along with the stone. Review it carefully to determine who issued it, and look up the standards for the sponsoring organization. If you have questions or concerns about the certificate, consider bringing it to a reputable jeweler for examination; jewelers may offer a quick consultation at no charge.
Examine the Setting
Stones commonly used in place of natural diamonds include cubic zirconia, moissanite, glass, quartz, and synthetic gems grown in lab environments. These are often placed in settings of low quality because they are worth less. Some warning signs that a piece of diamond jewelry may be fake can include metal that is flaking, pitting, or eroding, along with the absence of a stamp inside the setting to disclose the metal type.
Common Sense Tips for Diamond Buying
Some common sense measures can help prevent you from being pressured to purchase a gem that turns out to be something other than a diamond. It shouldn't be ridiculously inexpensive, or you'll get what you pay for. Real diamonds also will usually be mounted in an "open back" setting, which means that you can see around the rear of the gem and the back surface isn't coated with any silvery substance. True diamonds can also fracture or crumble because of inclusions, so hitting or crushing them as a test is not advised.
If a stone looks like the real deal, assess it for the four C's: Carat, Color, Clarity, and Cut. These can determine the value of a diamond by considering its size, visual appearance, and faceting. Blemishes inside the stone can degrade its appearance and stability, while a poorly-cut stone may fail to shine to its best advantage. Buyers should be aware that while these stones are famously depicted as white, they can be pink, yellow, blue, and other colors; these "fancy diamonds" can sometimes be more expensive if the color is unusually rich or rare.
Even many gemologists cannot distinguish "real" diamonds from cultured stones. Cultured diamonds have been artificially produced in a laboratory, not mined, yet they are chemically identical to naturally-formed rocks. Some companies are developing new kinds of identification methods for those who would like to purchase a mined diamond as well as buyers who prefer cultured stones.
Advanced certification is also available for consumers with ethical concerns about diamond sourcing. These programs attempt to track stones from source to end consumer to assure buyers that they are not purchasing so-called "conflict diamonds" that fund insurgencies. Reliability of these certificates is variable and, as with proofs of authenticity, it is a good idea to look up the organization that backs the program to learn more about it.