A diamond is evaluated through four different characteristics which can be combined in several ways changing the value of the gemstone. Here you are the “four C’s rule”.
The weight (and therefore the size) of a diamond, as all the gemstones, is measured in carats. The word originates from the seeds of the carob tree. In fact, those seeds were traditionally used to weigh diamonds. Later, a unique system was defined and one carat was set as 0.2 grams (one fifth of gram).
A carat is divided in 100 points. Therefore, a diamond of 25 points weighs a quarter of a carat, which means 0.25 carats. Here you are some example the approximate size against weight.
Almost all diamonds contain traces of not crystallized carbon. In fact, diamond originates from this element. The majority of these traces are not visible to the naked eye. They are called inclusions and are considered the diamond “fingerprints” that make every stone unique. At any rate, the less included the gemstone is, the rarer it is.
In the following paragraph we refer to the standard terminology of Confedorafi (Italian confederation of goldsmiths).
The term “clarity” is used to indicate how much the diamond has (or not has) imperfections. There are three main international systems to classify diamonds. GIA, CIBJO e HRD. A diamond without inclusions, both internally and externally, is classified FL (pure) by GIA system; other systems use the terms “loupe clean” or “internally pure”. However, the systems are equivalent for the grades under the top.
Here you are the clarity grading scale
Sometimes people are astonished in learning that diamonds can cover the entire colour spectrum. However, the majority of gems look slightly yellow or brown, although there are very rare diamonds that are defined colourless.
Even rarer are those diamonds that naturally have a well defined colour. These diamonds are called “fancy”. Among them, the most common colours are green, red, blue or amber.
Among the “four C” the cut is the one that can be mainly influenced by the human being. The others are solely influenced by nature. The ability of the diamond cutter discloses the gem beauty because the cut deeply influences the stone sparkle and focus.
As a matter of facts, it is the cut that allows the diamond to emanate all the light.
Precision and refinement of a diamond cut determine its brilliance, focus and beauty.
The choice of the cut shape is decided by the diamond cutter studying the shape of the raw diamond.
On the buyer side the cut is just a matter of individual taste; his or her choice is limited only by the diamond cutter’s ability and imagination.
The most common and well-known cut is the brilliant shape, however there are several other shapes; from the most common, such as marquise, drop (or pear), emerald, oval, baguette and heart; to the most imaginative and creative.