The most appreciated factor of a pearl's beauty. Good quality pearls have a lustrous gream. The Iridescence of pearls is called ‚luster’ or ‘Orient’. Pearls show this glamorous play of colours in delicate nuances due to the bow in their surface, enabling us to perceive their brilliance from every angle. The interaction of light rays and surface creates the iridescence, the so called ‘surface colour’ visible as a small circle on the pearl’s outer layer of nacre. The luster depends on the thickness of nacre, numerous layers encasing the nucleus. The layers of nacre act like tiny prisms, refracting light, so it appears as all the colours of a rainbow.
The luster is most important to asses the value of pearls. Intense luster increases the value.
This feature refers to the degree of surface perfection. Finer quality nacre is very smooth, and nearly blemish-free, however, most pearls have natural surface characteristics that serve to identify them and act as "mother nature's" fingerprints. The cleaner the surface, the higher luster produced and more valuable the pearls become.
he shape of cultured pearls is generally divided into round, symmetric and baroque.
Round shapes: almost and perfectly round
Symmetric shapes : Oval, button, drop
Baroque shapes: Semi baroque, baroque
To find a perfectly round pearl is extremely difficult. The closer the pearl’s shape is to a perfect round, the more valuable it is. In the end, preferences depend on the individual taste.
To judge the colour of pearls, a basic tone, luminosity and colour depth is considered. Akoya pearls show a spectrum covering shades of white, cream or soft pink. South Sea pearls shimmer in white, silver, pink or gold. Tahitian pearls are famous for their dark shades. A light grey is found, as well as gold, black-green to black.
The size of pearl depends on the size of the bead inserted into the mother oyster and the thickness of the nacre. The latter is one of the most important factors in determining quality.