The luster is one of the most important parameters influencing the price of pearl jewelry, it is based on two things: brightness, related to an ability to reflect the color, and inner shines, which is created by the reflection of light from the inner layers of aragonite, which makes the pearl shine unlike any other gem, and determines its value in jewelry industry.
Experts estimate the luster as low luster, medium luster or high luster. The brighter the freshwater pearl, the sharper is the reflection in the pearl's surface. The pearl with the low luster looks flat and is not as attractive.
Of course, the higher luster, the higher the price, but there are exceptions. First of all, the keshi pearls. As they are 100% made of mother of pearl, they have a perfect luster, but their price is lower than the price of cultivated freshwater pearl. Another exception - a thin layer of mother of pearl does not guarantee a high luster. For example, to some extent, genes of a mussel may contribute.
A very important parameter, as it affects the luster, and the higher the luster, the higher the quality. Ideally, the pearl should be absolutely smooth, clean (equally colored), without spots and with high luster. Unfortunately, pearls like that do not exist. At close examination, you will find few bumps, spots etc.
Some of these little defects can be hidden in a jewelry that will create a significant price increase. How can we determine which defects are important and which are not?
Very simple. Serous defects can (in future) ead to the deformation of a pearl. We are talking about scratches, deep "canyons" on the surface and so on. They can also provoke the layers of mother of pearl to fall of, or even worse, to destroy the entire pearl. Say, a relatively kind pressure may break the pearl in halves. It will require visiting a seller, looking for a new pearl to replace a broken one. What if we cannot find an adequate replacement? Then we will have to place an order to find it, which can be more expensive then buying a new piece of jewelry with the pearl of higher quality.
That's why fractions and deep scratches reduce the price significantly, even if the pearl is perfect by all other parameters. The less significant defects are small fractions and areas where the pearl is wearied off, which make these areas less shiny, or alter the color. Little spots, bubbles, color differences, all these cannot destroy the pearl, so it is not a big deal.
Of course, defects are bad. However, if you are buying the pearls without a certificate, these defects are an argument saying that you are buying a real pearl, not an imitation.