Polytechnic Association Proceedings. 53^ 



often beyond our recognition, they spring broadcast into life and 

 luxuriance. Dr. Berkeley says the surest remedy is to steep the 

 seed grain in some solution, which at once washes off a portion of 

 the spores, and poisons the rest. Many remedies have been pro- 

 posed, as simple water, salt, lime, sulphate of copper, corrosive 

 sublimate and arsenic. The best, perhaps, is sulphate of copper 

 (blue vitriol) in solution, dried off with quicklime. 



aOIEO ENGRAVING. 



The Loiidon Building J^eics contains an interesting description, 

 here condensed, of the art of cutting cameos, which is a species of 

 sculpture rather than engraving. There are two kinds of cameos, 

 one of which is of stone of different colored strata, so that the 

 raised figure is of a different color from the ground; the other is 

 of the couch shell. The shells are sawed into squares with saws 

 of soft iron, similar to those used by sculptors. These squares 

 are ground on their edges by means of a stone, so as to leave 

 them thicker toward the center. A cement is prepared by mixing 

 equal parts of melted Burgundy pitch and rosin; the end of a 

 stick, six or seven inches long, is dipped into this cement, and the 

 shell, while hot, is pressed on, and thus fastened to the stick; 

 after cooling, the shell is ready for cutting. To produce a like- 

 ness, the best way is to cut a profile on paper, lay it on the shell, 

 and trace it out. The best gravers — the harder the better — are 

 aloue fit for the work; and they are ground down to different 

 shaped points, some diamond, some oval, some round, and some 

 chisel-shaped. After the likeness or design is traced on the shell, 

 the next step is the blocking out, which is done either by hand or 

 with flat drills in a lathe, care beino^ taken to leave orroundwork 

 thick enough to finish up. In engraving a head, it is usual to 

 commence with the forehead, leaving the hair, which is one of the 

 most diflScult parts to represent, to be done last. No matter how 

 good the features may be, if the hair is badly executed, the whole 

 figure looks bad. Sculptured heads are the best models to study. 

 After the design or figure is finished with the graver, the cameo 

 is rubbed with pumice stone until the marks of the graver disap- 

 pear. The beautiful polish, for which cameos are justly admired, 

 is given by means of a stiff tooth brush and potter's clay, or whit- 

 ing and water. After the polishing is completed, the cameo may 

 be removed by warming the stick until the cement is softened. 



