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Only truly valuable when it is colourless and free of impurities Among minerals, it is the hardest, but fire burns it and a firm blow can shatter it. The name comes from the Greek adamas, meaning 'untamable', and the term was chosen in reference to its extreme hardness. Precisely because of this characteristic, the most admirable properties have been attributed to diamonds, such as those of making one invincible (especially those born in April) and of protecting one from enemies and adversities In the past, it was even believed that it was capable of 'sweating' in the presence of a poison, thus rendering attempts to poison it futile. Pure and transparent diamonds, colourless or with delicate pastel shades, are used in gemology and are among the most sought-after gemstones. Less rare varieties, as well as artificial diamonds, are instead used for industrial purposes.

Characteristics Diamond crystals are mostly in the shape of an octahedron or hexacisoctahedron (48 triangular faces), often with curved surfaces. Small triangular incisions called trigons can sometimes be observed on the faces of the octahedron. By twinning two octahedra, flat crystals in the shape of a bevelled triangle can be formed. Diamond consists of pure carbon: when heated, it burns releasing carbon dioxide. It is the hardest mineral known, but this does not mean that it is unbreakable: it can only be scratched by another diamond, but a firm blow can shatter it; in fact, it is brittle and flakes easily according to the faces of the octahedron.

Diamond has a very vivid, almost metallic lustre, which is called 'adamantine'. Many diamonds appear fluorescent under ultraviolet light.

How to recognise '4C'

This is undoubtedly the most important of the 4Cs, since the higher the quality of the cut, the better the combination of brilliance and fire of the stone.

The cut is also the only characteristic directly influenced by man. It is important to distinguish between the cut of the diamond, which is a purely technical matter, and the shape, which is a personal preference.

The round brilliant cut is the best known and most popular. Other brilliant cut shapes include the teardrop, the marquise (elongated with pointed corners), the oval and the heart. Another cut is the emerald. The princess is a square cut shape on the surface, the pavilion brilliant.

Behaviour of light in the diamond:

  1. When a diamond is cut to the correct proportions, light is refracted from one facet of the pavilion to the other and then reflected back through the crown and table of the diamond.
  2. If a diamond is cut with a pavilion that is too deep, some of the light is lost through the opposite side of the pavilion or from the bottom.
  3. If the pavilion is shallow, light is refracted onto the crown instead of the pavilion and is lost through the bottom of the diamond.

Colour is definitely the most subjective feature as different people prefer different colour tones. Diamonds come in a variety of white tones.

The colour assessment of a diamond for grading purposes is obtained by measuring the degree to which it approaches total absence of colour.

Those that come closest to colourless are very rare and are classified D, E, F and G while most are lightly coloured whites.

These are graded from the letter H to the letter L. Those graded M and above are visibly coloured. There are diamonds with a very strong pure colouring that are extremely rare and are called 'Fancy'. They can be pink, blue, green, deep yellow.

No two diamonds in the world are the same. Each has its own precise identity due to the presence of small traces of carbon or small crystals of a different nature that have become trapped during the crystallisation process.

They are called inclusions and are structural inhomogeneities that are considered 'natural footprints'. Their number,

colour, size and position determine the diamond's degree of clarity. However, most inclusions are not visible to the naked eye: a ten magnification lens and the jeweller's experience are required.

The weight of diamonds, like that of other gems, is expressed in carats. The word carat originated in antiquity when carob seeds, with their surprisingly regular weight, were used to weigh gems.

Currently, the carat is a decimal unit of measurement that corresponds to 1/5 of a gram, divided into 100 points.