96 ANNUAL OF SCIENTIFIC DISCOVERY. 



paper is then laid over the leaf, and rubbed with a soft pad, which presses 

 the leaf in contact with the stone, and makes the impression. The stone 

 is now subjected to the usual lithographic processes, as if it were a draw- 

 ing. 



2d. The metallic plate process, printing from a raised metal siirface like a 

 wood-cut or type. " We take a leaf and prepare it in the manner above de- 

 scribed, substituting, however, for the lithographic ink, a composition made 

 by melting together about equal quantities of, ' etching ground/ ' common 

 tallow/ or ' balsam of Judea/ and ' sweet oil/ and for the sheet of writing 

 paper a porcelain or metallic plate, which plate is placed over warm watei. 

 The leaf is now laid upon the metallic plate. A piece of paper is placed 

 over the leaf and rubbed as before. Upon removing the paper and leaf, a 

 true impression of the latter is made upon the plate, and all that remains to 

 be done is to remove the metallic ground surrounding the impression and 

 intervening between its parts, which is accomplished by the well-known 

 etching processes as that of employing dilute acids, or by the agency of gal- 

 vanism, the latter being preferable. The plate is now engraved, and a true 

 convex image of the leaf is produced. The plate may then be printed from 

 as if it were type or a wood engraving." 



3d. The ordinary copper plate or cylinder process, the engraving being con- 

 cave. " We take a metallic plate, and thinly coat it with ' etching ground." 

 The leaf is pi-epared by being dabbed with oil paint, the same as that used 

 by artists, which has been spread over a sheet of paper. The leaf is placed 

 upon the etching ground, and a piece of paper laid over it, which is rubbed 

 as before. We now remove the paper, and in about one minute the leaf 

 also. Now, where the oil paint has touched the ' etching ground/ the latter 

 is dissolved, which is at once carefully wiped off with a soft rag, the copper 

 now appearing through where the ground is removed. The plate is now 

 washed with soap and water to remove all remaining grease, and then sub- 

 jected to the usual etching processes. In this case the image of the leaf is 

 concave, and is printed off by the usual copper-plate printing process. 

 When rollers or cylinders are employed instead of plates, the process is 

 similar." 



The ordinaiy mode of etching by acids does not answer, as before the 

 ground is eaten away sufficiently to enable the com^ex figure of the leaf to 

 be printed from, the finer parts arc destroyed by the lateral action of the 

 acid. By the electrical etching, however, the results obtained are highly sat- 

 isfactory. The results from endeavoring to eat off, by the agency of oils, 

 " etching-ground," from a plate which had been covered with this substance, 

 the image being concave, are at present uncertain. This method of produc- 

 ing similar results seems, however, to bid fair for success, viz., that of 

 taking the impression of the vegetable object in grease upon a steel .plate, 

 and etching it, not very deeply, by electricity, then pressing this etching into 

 soft copper (as is done in the preparation of cylinders for calico printers), 

 after which the etching on the copper plate or cylinder is deepened by the 

 ordinary re-etching process. 



A word must be said upon the cost of the process, as this necessarily 



