/ 

 MOTHER OP PEARL AND ITS USES. 221 



Pearl shells will average about six inches in diameter, and are so ex- 

 tremely hard, that they have to he wetted, while being cut with a circular 

 saw, to prevent the saw being softened by the heat. This is a dirty occu- 

 pation, and is accompanied by a " very ancient' and fish-like smell," 

 elicited by the heat from the shell itself. The pieces have afterwards to be 

 ground down on stones singly, and by hand, to a level surface and a required 

 thickness. This tedious process aids in making shell a costly covering for 

 cutlery ; and, as the substance is both hard and brittle, when the handles 

 or scales are fluted or carved, the price is, of course, still more enhanced. 

 The beautiful iridescent appearance of the pearl shells is attributed to their 

 laminated structure, which disposes their surfaces, in minute furrows, that 

 decompose and reflect the light, and, owing to this lamellar structure, 

 admit of being split into leaves, for handles of knives, counters, the pur- 

 poses of inlaying, &c. ; but they are very apt to follow, and even to exceed 

 the curvature of the surface, and therefore splitting is not much resorted to ; 

 but the different parts of the shell are selected to suit the several purposes 

 as nearly as possible, and the excess of thickness is removed upon the 

 grindstone, in preference to risking the loss of both parts, in the attempt to 

 split them. The usual course in preparing the rough pearl shell for the 

 arts is, to cut out the square and angular pieces with the ordinary brass- 

 back saw, and the circular pieces, such as those for buttons, &c, with the 

 annular or crown saw fixed upon a lathe mandrel. The sides of the pieces 

 are then ground flat upon a wet grindstone (running in soap and water), 

 the edge of which is turned with several grooves, as the ridges are con- 

 sidered to cut more quickly than the entire surface, from becoming less 

 clogged with the particles ground off. The pieces are finished upon the 

 flat side of the stone, and are then ready for inlaying, engraving, polishing, 

 &c, according to the purposes for which they are intended. Cylindrical 

 pieces are cut out of the thick part of the shell, near the joint, or hinge, 

 and they are rounded upon the grindstone, ready for the lathe, in which 

 they may be turned with the ordinary tools used for ivory and the hard 

 woods. 



The articles made from this shell are comparatively expensive, 

 in consequence of the large amount of labour spent in reducing or 

 grinding the shell to any given size or shape, a process which even- 

 tually will, no doubt, be rendered more facile by the introduction of 

 machinery. 



In the process of polishing, which is simple and inexpensive, the shell 

 articles are first smoothed with Trent sand or pumice-stone and water, or 

 a buff- wheel or hand-polisher, and then finished off with rotten-stone. The 

 latter powder, although sometimes used with oil or water, is more frequently 

 moistened with a little sulphuric acid, nearly or quite undiluted ; this pro- 

 duces a far more brilliant polish, which may possibly arise from the partial 

 destruction of the surface, thus developing in a more decided manner the 

 striated formation of the pearl shell, and to which peculiarity of structure 

 its variegated lustre is ascribed. 



