How to choose a diamond

In order to estimate the value of a cut diamond we must evaluate 4 main characteristics, the 4C, coming from the initials C of the English words: carat, color, clarity, cut.

Carat
The carat indicates the weight of the diamond expressed in carats (1ct = 0.2 gr). The value increases exponentially with the weight ( ex. a 2 ct diamond has a price that is aproximately 4 times the price of a 1 ct diamond of the same quality )

Color
Color is generally indicated by a letter of the alphabet, starting from D (maximum transparency, total absence of color) down. D, E, and F indicate an exceptional white, G, H, and I indicate a white color, and from J down you will begin to perceive shades of color, usually yellow or brown. Observing a color difference between two letters is a difficult exercise even for an expert.

There are also diamonds that have pleasant colors, highly sought after and expensive. In order of increasing value, these colors are brown, yellow, green, orange, pink, blue and red. 

Clarity
The Clarity feature indicates inclusions (which are always present). Inclusions should only be checked with a magnifying glass or microscope that magnify 10 times, not more not less.

The highest degree of clarity is generally indicated by F ( completely flawless without internal inclusions and external defects). It is followed by IF (Internally Flawless ,without internal inclusions), VVS1 (very very small grade 1 inclusions), VVS2 (very very small grade 2 inclusions), VS1 (very small grade 1 inclusions), VS 2 (very small grade 2 inclusions), SI1 (small grade 1 inclusions), SI2 (small grade 2 inclusions), I1 (grade 1 inclusions), I2 (grade 2 inclusions, which compromise transparency), I3 (grade 3 inclusions, which compromise transparency and stone integrity). Usually, with a 10x magnifying glass you will see the inclusions starting from SI1. Even for an expert it is extremely difficult to detect the differences between the first 3 degrees of purity.

Cut
The cut is an important factor, and the effects are obvious even to non-experts. Excellent is the best indicator, followed by Very Good, Good, Fair and Poor. You should always choose a diamond with an Excellent or Very Good grade; a lower quality visibly affects all the aspects of its appearance.

Most diamonds have the so-called modern brilliant cut. This is a 57-faceted round cut, developed in the 1920s by engineer Marcel Tolkowsky and requires about 3-4 days of work for a 1 carat diamond.