Anyone looking to buy a beautiful diamond or a jewel set with diamonds of respectable size (0.2 carat) must understand the quality scale applied to diamond in order to classify and estimate their value.

The 4Cs of Diamond for Carat (weight), Color, Clarity (purity) and Cut is an international classification rule valid for all white diamonds.

All jewelers, diamond dealers and gemologists refer to it to understand each other when comparing the quality and price of diamonds.

And so, it's your turn to understand the 4Cs of diamond to choose the best your diamonds.

quality criterion diamonds


  1.   The carat measures the diamond weight
  2.   The diamond color is measured from the letters D to Z
  3.   What is the diamond purity ?
  4.   The quality of the diamond cut, determining factor of its brilliance
  5.   The certificate


 Free Bonus : Download our complete guide on Diamond (fr). 

You'll discover all you need to know to buy diamonds jewelry online or in store.


engagement ring diamonds engagement ring diamonds engagement ring diamonds

1. The carat measures the diamond weight 

The carat is the measurement unit for the diamond weight, one carat is equivalent to 0.2 grams.

This classification criterion of diamonds is the easiest to apprehend since it depends on the stone dimensions. So the bigger the diamond weight, the bigger the diamond (and expensive) at equal quality.

I recommend this article which presents you in the form of tables the relationship between the dimensions of a diamond and its weight for diamonds cut round brilliant and cut in princess.

weight size diamonds

This table gives an order of weight magnitude of a round diamond according to its diameter, because the diamond height modifies these values. (source image)

Note that we often compare diamonds of the same weight (or near) according to the criteria that follow.

2. Color, a subtle criterion for diamonds classification

Sign of purity and rarity, the more a diamond will be colorless (white) the more expensive it will be.

The international color scale of white diamond includes 23 grades graded from D (perfectly white diamonds) to Z.

However, only gemologists and diamond certification experts are able to appreciate the subtle shades of shade that exist from one letter to the next.

colors diamonds chart

It's because it's difficult for a non-expert to differentiate the hue shades that are grouped by color family diamonds as we see below.

GIA colors scale

This color scale used by the GIA classifies diamonds into 5 color families ranging from perfect white to light yellow.

Note : colored diamonds also called fancy diamonds, are not classified according to this scale.

3. Purity indicates the diamond degree of imperfection 

All diamonds have imperfections. These imperfections are inclusions at the heart of the diamond structure that appeared during the diamond formation.

The determination of the diamond purity is done under special light with a magnifying glass X10. So when we talk about impurities, we must know what we are talking about because in most cases they won't be visible to the naked eye nor affect the diamond brilliance.

Here is a classification table of diamonds according to their degree of purity

diamond clarity chart

4. The cut quality of the diamond greatly affects its brilliance

The diamond can take many geometries to sublimate its brilliance and exploit at best the rough diamond extracted from the mine. It's the round and princess cut that are the most used in jewelry. Here are the most common cut shapes :

differents cut

It's the cut quality of the diamond (whatever its shape) that will maximize the brilliance of it. It's the only one of the 4 evaluation criteria of the diamond which depends on the man's work. Indeed, a bad cut can either generate too much loss of rough diamond or not exploit at best the brilliance of it.

The diagram below summarizes what is a well-cut round diamond and the importance of these proportions for maximum brilliance of it, the path of light depends directly on its cut quality.

diamond cut diagram

The classification scale for diamonds according to their cut quality is as follows :

clarity cut diamonds

5. Guarantee certificate of diamond

Starting at a certain price or weight (ranging from 0.3 to 0.5 carat depending on the jeweler) a diamond guarantee certificate is delivered at the time of purchase.

This certificate is established by an independent laboratory which notes according to the 4C rule the quality of the diamond sold.

The most famous of these gemological laboratories is the GIA, here is an explanatory video on reading the reports they provide with the diamonds they certify.

 Free Bonus : Download our complete guide on Diamond (fr).

You'll discover all you need to know to buy diamonds jewelry online or in store.


For further :


August 05, 2019 — Hugo Maherault

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