590 APPENDIX 



No pearl is completely transparent, but among different specimens there are many 

 degrees of translucency. Different qualities of pearls are described, as in the case also 

 of diamonds, as being of different " waters,'" and the difference between them depends 

 upon the amount of light transmitted in each particular case. 



The colour of a pearl has an important bearing on its value. Those used for 

 ornaments are mostly white, yellowish- white, or bluish- white, more rarely reddish- or 

 blackish-grey. A pearl with a perfect pearly lustre, or, as the jewellers say, a "ripe" 

 pearl, has the colour of the mother-of-pearl layer in the shell in which it was formed, but 

 each pearl has sometimes a certain individuality as regards colour. The pearls formed by 

 the true pearl-oyster {Meleagi-'ma margaritifera) are white, and it is these and the silvery, 

 milk-white pearls which are most valuable. The smaller the dimensions of the microscopic 

 irregularities in the surface of a pearl the finer will be its appearance, for on these 

 rugosities of the surface depends the scattering of the incident light and the gleaming 

 white colour of the pearl. The fine colour of " ripe " pearls is due partly also to the fact 

 that they consist wholly of colourless nacre. Should there be present a nucleus consisting 

 of the substance of the prismatic layer, it shines through the strongly translucent nacreous 

 layer, making the pearl appear dull and dark, and this is specially the case when the outer 

 pearly layer is thin. Such grey or brown translucent pearls are described as being 

 " unripe.'" Of a large and beautiful Indian pearl it was said that it rolled about on a 

 sheet of white paper " like a globule of quicksilver," surpassing even the metal itself in 

 lustre and whiteness. Silvery, white, transparent pearls of this description are classed as 

 pearls of the finest water : they always possess a thick outer nacreous layer. Many true 

 pearls, however, are slightly tinged with yellow, or are even of a pronounced yellow colour, 

 this being more frequently the case with those from the Persian Gulf than with the pearls 

 from Ceylon. These yellowish pearls are much esteemed in Asia, India, China, &c., being 

 considered to be less perishable than the white. It has been said that white pearls, if 

 enclosed in the shells of decaying molluscs, acquire a yellow tinge, but according to special 

 research in this direction this is not, or at any rate not always, the case. Pearls with a 

 faint bluish tinge are also frequently met with, this colour being the same, as is also the 

 case with yellowish pearls, as that of the mother-of-pearl layer of the shell in which such 

 pearls were formed. 



Beautiful black pearls are sometimes found in molluscs from the South Seas and the 

 Gulf of Mexico, having been formed probably near the border of the mantle. They are 

 the hardest of all pearls, and when of a beautiful and uniform colour and perfect form are 

 worth almost as much as pearls of the purest white. Such black pearls are used in Europe 

 in mourning jewellery. Intermediate between white and black are lead-coloured pearls, 

 which are not uncommon. Reddish-brown pearls containing some ii-on come from Mexico. 

 The hammer-oyster (Malleus) from the Gambia Islands yields pearls with a bronze-like 

 sheen. Not infrequently greyish-brown pearls, in which the nacreous layer is absent, are 

 found in the fresh-water pearl-mussel, Unio margaritifer. In the fan-mussel. Pinna iwMlis, 

 are found light and dark brown pearls, in some of which also the nacreous layer is absent, 

 the outer coat consisting of a substance corresponding with the prismatic layer of the 

 shell. The same shell, however, may contain garnet-red pearls, in which the pearly nacreous 

 layer is present, and which are highly prized both by the Hindoos and by the Jews. Pale, 

 rose-red pearls with delicate white wavy lines, like the most beautiful pink velvet, come 

 from the Bahamas. Pale blue pearls are often met with in the edible mussel {Mytilus 

 edulis) ; greenish-white and pale rose-red pearls in Spondyhis gadaropufi ; violet in the 

 ark-shell {Area nom) ; purple in Anomm cepa ; and lead-coloured in Placuna placenta. 



