 Since mussels may live for many years, the process may be repeated; however the amount of nacre produced continuously falls with age, and most cultivators harvest only twice.Keshi pearls consist of solid nacre, and tend to have high luster as a result.All nacre colors typical of the mollusc under cultivation may be represented among keshi pearls harvested from the same, but in the case of Akoya pearls a larger portion of keshi is usually grey than of bead-nucleated pearls.