514 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 

 A NEW PROCESS OF ENGRAVING ON COPPER. 



The Hydrographic Office at Paris has begun a process of 

 engraving on copper which promises by its rapidity and the 

 moderation of its price to be very widely useful. It consists, 

 in substance, first, in covering a plate of copper with a thin 

 shell of adhering silver, upon which is spread a thin layer of 

 colored varnish ; second, in drawing thereon, with a dry point, 

 the lines, topography, and lettering, precisely as one engraves 

 with a diamond upon stone; third, in corroding the traces by 

 means of the perchloride of iron. 6 B, LXXVIIL, 1535. 



SLATE EOR ENGRAVERS. 



As a matter of interest to wood-engravers, we note the re- 

 ported discovery that plates of polished slate may be used in 

 wood-engraving as substitutes for box-wood. It is declared 

 that such engraved plates will furnish over 100,000 impres- 

 sions without loss of detail; and, further, that they will not 

 warp, and are not affected by either oil or water. The one 

 drawback which they possess, however, is the fact that they 

 are readily scratched; an objection from which even wood 

 is not entirely free. 



FRENCH METHOD OF ENGRAVING ON WOOD. 



A French method of engraving on wood consists in first 

 covering the block with a layer of gelatin (0.39 grammes to 

 31 grammes of water) by means of a soft brush. When this 

 coating is dry, it is covered, in the dark, with a solution pre- 

 pared of (1) red prussiate of potash, 7.80 grammes; water, 

 62.20 grammes; (2) ammonio-citrate of iron, 9.10 grammes 

 in 62.20 grammes of water. These solutions are mixed and 

 filtered, and the mixture is kept in the dark. After the lay- 

 er is dry, it is exposed under a negative from ten to twelve 

 minutes, and washed with a soft sponge, when a blue image 

 appears. If thus prepared the coating does not shell off un- 

 der the graver. 5 A, January, 1875, 98. 



GOLD, SILVER, AND BRONZE INKS. 



Most of the gold and silver inks on sale are so wanting in 

 brilliancy and fluidity, and retain their stickiness to such an 

 extent after use, that shell-gold and shell-silver are generally 



