Until a few years ago, people who were interested in buying a diamond had to blindly trust the experience and honesty of the seller. But nowadays, globally, there are very strict standards to classify gemstones, and it’s a great system to protect the buyer.


The 4 Cs stand for the four main characteristics used to classify diamonds and determine their values:

  • Carat
  • Color
  • Clarity
  • Cut


Transparent gemstone – which are the purest – are defined “colorless” and marked with the letter D. Then there are the “near colorless” and “slightly tinted” gemstones.

Some countries, European regions, cities or institutions (Antwerp, New York, Switzerland, Scandinavian countries and France) adopted various sub-nomenclatures for these 3 classes of colors. Diamonds can have almost every color due to impurities or structural imperfections: amber yellow and brown are the most frequent; red, rose and blue are the rarest.

It is worth noticing that colorless diamonds do not seem so at a first glance, because the facets reflect the surrounding colors. As other colorless gemstone, the colors change rapidly when you move them. This effect, which is very intense in diamonds, is called “liveliness” or “fire”.

Black diamonds are not really black. They have several incisions that make them seem dark – even if nowadays, with such growing demand for these gemstones, diamonds of poor quality are treated artificially to obtain that color.

The Gemological Institute of America (GIA) classifies yellow diamonds with low saturation and brown diamonds as diamonds in the normal scale of color, and applies an evaluation scale from D (colorless with the highest purity) to Z (light yellow).

The GIA also classifies diamonds with an intense color with the term “fancy”.

 The rarest coloring is that of red or rose diamonds, which are never very big, followed by the blue ones. Green diamonds are also very rare.


It consists in the classification of the dimensions and number of impurities of the gemstone, verified by a test with a 10x magnifying glass and expressed by one of the following acronyms:

  • VVS1 / VVS2 Very Very Small Inclusion (very hard to see)
  • VSI1 /VSI2 Very Small Inclusion (hard to see)
  • SI1 / SI2 Small Inclusion (easy to see)
  • P1 / P2 / P3 Piqué (visible to the naked eye)


Before starting their work, the cutters will have to take into account the shape of the rough gemstone, the shape that they want to obtain, the proportions of the cutting, and the symmetry. 

According to the quality of the cutting, diamonds are divided into categories:

  • “excellent” (perfect symmetry/proportions)
  • “very good” (very good symmetry/proportions or irrelevant flaws);
  • “good” (lesser symmetry/proportions);
  • “fair” (symmetry/proportions with relevant flaws)
  • “poor” (mediocre, with big and/or several flaws).


Diamonds are measured in carats, and 1 carat is 0,2 grams. The carat can also be divided into points, which correspond to 1/100 carat. In the past the “grains” were also used, and they corresponded to 1/20 gram.

The term comes from qīrāṭ (قيراط , “the 24th part”), in turn borrowed from the Greek kerátion (κεράτιον, a diminutive of keras [κέρας] that is, “horn”), “carob seeds”, used for their extraordinary uniform mass, about 1/5 gr.

From the ancient times since the Middle Ages, the carat has been used to weight very little quantities, and today it is the unit of measurement for diamonds, gemstone in general, and gold.

The carat was reported and precisely defined only in 1832 in South Africa, the country that mined and exported the highest amount of diamonds in the world. In that occasion, they defined the ratio of the carat with the decimal metric system: weighing some carob seeds on a scale with equal-length arms and averaging the results, they obtained a value of around 0,2 grams. Eventually, at the “4th General Conference on Weights and Measures” in 1907, the current definition of the so-called “metric carat” was adopted as a mass unit of 0,2 gr.