FRESH-WATER MUSSELS AND MUSSElv INDUSTRIES. 87 



or in injury to machinery would more than counterbalance the saving of material. 

 Nevertheless, all factories are not equally efficient, and some waste occurs that could 

 be prevented by watchful and judicious management and by proper training of labor. 

 It will not be out of place to illustrate this fact by the use of a few photographs with 

 brief explanation. 



Plates XLIV, XLV, and XLVI illustrate the progress in good cutting. 



Plate XLIV, figure i , shows a single shell where the cutter, though exerting some care 

 to avoid waste of material, showed a lack of experience or judgment. The blanks were 

 irregularly and poorly spaced. In some cases, too, the blanks were spaced too closely, 

 so that true circular buttons could not have been obtained. Contrast this with the 

 lower figure on the same plate, where the cutting was in rows, with best practicable use 

 of shell. 



Plate XIvV includes shells from various plants where the cutting is done with 

 more than average economy ; the shell in the lower right-hand corner illustrates a danger 

 in too close cutting, where, because of overlapping a space previously cut, the cylin- 

 drical saw was caused to unroll with more damage than a slight loss of material would 

 have entailed. The shell was evidently thrown away in disgust. The avoidance of 

 the rim blanks in the heavier shells of this illustration may be noted. Blanks obtained 

 from the rim of such shells have so much bevel that they will not work successfully in 

 the further processes and are liable to cause injury to machinery. 



Plate XLIV, figure 2, and Plate XLVI illustrate the most economical cutting 

 feasible under present conditions, and also show how shells are used to practical 

 advantage by double cutting; that is, by taking out the larger lines first and then 

 removing the smaller lines. Plate XLVI, figure 2, shows an excellent spacing of blanks 

 in a very favorable shell. 



WASTE DUE TO EXCESSIVE THICKNESS. 



A serious source of waste is found in excessive thickness of shell. If a shell is of 

 sufiicient thickness for buttons throughout, and in no part of excessive thickness, the 

 waste consists in the spaces between blanks and the unutilizable portions of shell such 

 as the hinge, umbones (knuckles), and rim. Many otherwise excellent shells, however, 

 are very thin at the tips, while the blanks from the forward portion of the shell are so 

 heavy that from one-half to three-fourths or more of the thickness must be ground off 

 (Pi. XXXVII, fig. 2). It is unfortunate that such blanks can not be split. Very 

 thick blanks from ocean-pearl shells may readily be sliced or split into as many blanks 

 as desired ; but in the fresh-water mussel shells there are irregularities of stratification, 

 or faults, in the shell which cause the splitting to occur in such irregular fashion that 

 with any method or device so far employed the waste is quite out of proportion to the 

 saving. 



Between shells which produce 700 gross of buttons per ton and those which produce 

 1 ,000 gross per ton there is a distinct difference in economic value, assuming quality to 

 be the same ; also, there is a saving in the working of lighter shells, since there is evidently 

 a useless waste of time involved in the sawing of thick shells and in the subsequent grinding 

 away of excessive thickness. Furthermore, the heavy shells are of much slower growth. 

 Assuming an equal quality from shells which are lighter and more nearly uniform in 



