Miscellanies. 385 



9. Method of 'permanently fixing, Engraving, and Printing from 

 Daguerreotype Pictures : by Dr. Berres, of Vienna. 



The method of permanently fixing the Daguerreotype picture with 

 a transparent metal coating, consists in the following process : — 



I take the pictures produced in the usual manner, by the Daguerre- 

 otype process, hold them for some minutes over a moderately-warmed 

 nitric acid vapor, or steam, and then lay them in nitric acid of 13° to 

 14° Reaumur, in which a considerable quantity of copper or silver, 

 or both together, has been previously dissolved. Shortly after being 

 placed therein, a precipitate of metal is formed, and can now be 

 changed to what degree of intensity I desire. I then take the helio- 

 graphic picture coated with metal, place it in water, clean it, dry it, 

 polish it with chalk or magnesia, and a dry cloth or soft leather. 

 After this process, the coating will become clean, clear, and transpa- 

 rent,* so that the picture can again be easily seen. The greatest care 

 and attention are required in preparing the Daguerreotype impres- 

 sions intended to be printed from. The picture must be carefully 

 freed from iodine, and prepared upon a plate of the most chemically 

 pure silver. 



That the production of this picture should be certain of succeed- 

 ing, according to the experiments of M. Kratochwila, it is necessary 

 to unite a silver with a copper plate ; while upon other occasions, 

 without being able to explain the reason, deep etchings or impres- 

 sions are produced, without the assistance of the copper plate, upon 

 pure silver plate. 



The plate will now, upon the spot where the acid ought not to have 

 dropped, be varnished ;t then held for one or two minutes over a 

 weak warm vapor or steam, of 25° to 30° (Reaumur) of nitric acid, 

 and then a solution of gum arabic, of the consistence of honey, must 

 be poured over it, and it must be placed in a horizontal position, with 

 the impression uppermost, for some minutes. Then place the plate, 

 by means of a kind of double pincette, (whose ends are protected by 

 a coating of asphalt or hard wood,) in nitric acid, at 12° or 13° (Reau- 

 mur.) Let the coating of gum slowly melt oiF or disappear, and 

 commence now to add, though carefully and gradually, and at a dis- 

 tance from the picture, a solution of nitric acid, of from 25° to 30°, 

 for the purpose of deepening or increasing the etching power of the 

 solution. After the acid has arrived at 16° to 17° (Reaumur,) and 

 gives off a peculiarly biting vapor, which powerfully affects the sense 

 of smelling, the metal becomes softened, and then generally the pro- 



* We do not well see how a film of metallic silver, however thin, can be trans- 

 parent. 



t This and some other passages, are a little obscure. 



