FISHERY RESOURCES OF THE PHILIPPINE ISLANDS. '.)<) 



DETEBMINA'I'lON AND VALUATION OF PEARLS. 



Pearls have a hardness of [, they are so compact that they do not 

 break when stepped upon; ilieir spccillc gravity is 8.65 to 2.68. To be 

 of much value they must be round or drop-shaped and either pure white, 

 or dark, or of a golden color, with a peculiar luster and slight trans- 

 lueency. They must be free from spot, speck, or blemish. As they are 

 formed, layer upon layer, around a central point, like the layers of an 

 onion, they are sometimes peeled or "doctored" to remove spots or flaws, 

 in the hope that the new layer will be of better luster. Such pearls are 

 obviously of much less value than those found perfect, in their natural 

 condition. Howe\er, any such tampering with a pearl can usually be 

 detected by the use of a good glass, which shows any minute band-like 

 stripes or slight scratches. It is also a very easy matter to detect whether 

 a trifle more than one layer of a pearl has been taken off, and equally as 

 easy to tell the difference between a pearl that has been ground into a 

 round shape and one naturally round; such specimens are of but little 

 greater value than marbles. The following is a table of the actual size 

 of pearls of from 0.1-296 to l.ii44 grams (2 to 30 grains). 



Grains. Grains. Carats. 



2 # 3 # -^ 



10 



,3 ^ lA 



25 fl^Bt 30 



Fig. fi. — Exact sizes of pearls from 

 to 30 grains in weiglit. 



