The luster of a pearl represents its brilliance. It is with the shape of a pearl, its diameter, its color, and the quality of its surface one of the five criteria for classifying the pearls. However the nacre is contrary to other criteria such as diameter, very difficult to measure, and therefore to quantify and therefore to classify. Indeed, the nacre is not something concrete but something very subjective and very dependent on ambient light. This is why experts trying to quantify the luster of a pearl study all the pearls in a windowless room, always with the same electric light on the ceiling and therefore the same light conditions.
The nacre represents the reflection and brilliance of a pearl. The more the pearl has a significant reflection and it is clear and precise, the more experts will say that the pearl has a very bright luster.
There are several degrees of brilliance. These same degrees are used for all the criteria for classifying the pearls and therefore to classify the pearls themselves.
Origin of the luster
It is important to note that the luster of a tahitian pearl does not depend on the thickness of its mother-of-pearl. Thus, the pearls of Australia, having a very thick nacre, do not have a more or less shiny luster than other pearls. On the contrary, the quality of the nacre is more about the quality of the oyster and the water where the pearl develops.
This is why the choice of oysters is very important to develop pearls with a very good quality nacre. Oysters that are too large are also a hindrance to the quality of the nacre because the pearl will take too long to touch an edge of the oyster. In this case, the pearls will be harvested too often before they have even touched an edge of the oyster and therefore without having developed and used their abilities in terms of developing the quality of shine, luster.
The nacre is measured once the pearl has been washed and dried for several hours. However, shine can deteriorate over time. Again, it is the pearls with the highest degree of brilliance that will do best because their nacre will degrade much less quickly and the same for their brilliance.
The brilliance of a pearl is very special because this criterion is not found in other gems such as gems.