Buying Diamonds – 5 C’s & 4 Tests

We all know that diamonds are touted as being a girl’s best friend – but with diamonds having a 20% increase in value within the last couple of months or so – they are also being looked at as an investment. Note: Investment diamonds are usually of a larger size, preferably certified.

So for those that are out there scouring the garage sales, flea markets and estate sales for gold and silver to turn into cash – why not add diamonds to the list. Granted you’ll probably only find them in jewelry – and they’ll probably be of a smaller size – but if you find enough you may be able to make a little extra money by selling them to a jewelry maker or someone that repairs jewelry . . .  and there’s always the chance you’ll get lucky and find the ‘big one’.

What to Look for in a Diamond – 5 C’s

Cut – this is the shape and can affect the size and brilliance of the diamond. Typical cuts are: Round, Oval, Pear, Heart, Marquise and Rectangular / Square. When looking at cut you want to look for the proportions and finishing of the cut.

Carat – this is the weight of the diamond. Diamonds are measured as carats, grams or milligrams. A diamond weighting 1 carat would be the same as a diamond weighting one-fifth of a gram or 200-milligram. The term ‘point’ is also used to refer to diamond weight, with one point equaling 0.01 carats.

The carat weight is important because it has a direct affect on the value of the diamond. The higher the carat the higher the value, ie., price.

Color – you may think that diamonds are colorless, however, they come in many different colors – these are referred to as fancy – with the ‘clear-colorless’ one we see set in most jewelry being called ‘white’. Other colors you might see are yellow, pink, black, green, orange, blue, brown and the most valuable – red.


* – Blue diamonds do occur naturally in nature, however, you may find that most ‘affordable’ blue diamonds are irradiated.

** – Brown diamonds come in different shades and are sometimes referred to as cognac colored. And there are some retailers that refer to them as ‘chocolate’.

Clarity – refers to the degree a diamond is free from external marks (blemishes) and internal flaws (inclusions). Most of the time you would think the buyer would want as flawless a diamond as possible, not true. A flawed diamond can represent a lower price, ability to identify your diamond, and sentimental reasons.

There are flaws to avoid when buying diamonds –

  • Large milky or cloudy areas
  • Deep cracks
  • Large Chips
  • Big white, black or blotches that can be seen with the naked eye

Confidence – if buying from a retailer you want to know you are purchasing a certified diamond as well as having confidence in the seller.

If buying diamonds from someone other than a certified retailer, most buyers will not know the difference between a diamond and an imitation.

Testing – Diamond?  Glass?  CZ?

The best way to test a diamond is to have a diamond tester.  But if you don’t have access to your equipment while out shopping, here are a couple of simple ‘tests’ that may help –

See-through test – looking at the stone face up, if you can see through it, it’s probably and imitation. The exception would be if a real diamond were poorly cut or the presence of dirt or grease allowed you to see through it. You can also try placing the stone face down over newsprint, if you can read the letters through the stone – again, probably imitation. Note, some diamonds set in antique jewelry will allow you to see through them due to the different cut (rose or mine cut) and the presence of the large culet (cut on the bottom parallel to the top of the stone)

Tilt test – Tilt the stone against a dark background and look for an obvious dark, fan shaped area. If you see such a fan, chances are the stone is imitation. This test is easier to perform on mounted stones and also works best on round cuts.

Rainbow test – move the stone under a light and note the flashes of rainbow colors compared to a diamond. If the colors are more obvious, chances are the stone may be synthetic; less obvious, the stone may be imitation.

Closed back test – When looking at jewelry set with diamonds, check the back. If the bottom of the stone is blocked or enclosed in metal it is probably imitation as most diamonds have at the very minimum the bottom partially viewable. However, an open back does not guarantee the stone is a diamond. Note: In antique jewelry prior to the eighteenth century, it was common to put a foil backing on diamonds to improve on their brilliance. Current styles where channel set diamonds are used, jewelers have used solid backs to increase the rigidity of the setting.

Price test – if the stone is being sold at an unbelievably low price – chances are it might be imitation, stolen – or maybe you just found the find of the century.


This is a very brief overview of diamonds and what to consider when buying and how to test. If you want to learn more about buying diamonds we recommend The Diamond Ring Buying Guide  by Renee Newman and we also would recommend getting a Presidium Diamond Tester – it positively tests for  diamonds vs glass or other gemstones.  We’ve been using one for many years and found it totally reliable.


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