V] PEARLS 63 



are known to exist. White, or as nearly white as is 

 possible, is usually regarded as the most sought after 

 and perfect tint. Colour alone, however, is not nearly 

 sufficient and there must be in addition a peculiar 

 kind of lustre. 



It is this combination of tint and lustre that has 

 made the Ceylon pearl of such great fame and value, 

 and although equally good specimens often occur in 

 other places, even in fresh- water molluscs, on the 

 average the Ceylon pearls seem to be better than 

 those from most other localities. Many of the colour 

 effects are not due to the presence of actual pig- 

 ment but rather to reflection and refraction pheno- 

 mena. Tlius one may have white pearls with a blue, 

 a green, or a pink sheen, although yellow is by far 

 the most common. Other pearls with more definite 

 colours and darker tints generally possess little or 

 no lustre, and some of these would hardly be con- 

 sidered true pearls at all by dealers. 



This often applies to the pearls found in the 

 common edible mussel. In fact, supporting this 

 remark, we find in the glossary of one book on pearls 

 a definition of true pearls as follows : " Pearls formed 

 of nacre as distinguished from similar formations 

 which are not nacreous." It is not at all necessary 

 for a true pearl to have any of the nacreous layer 

 represented in its structure. 



The black pearl does not seem necessarily to be 



