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ENGRAVING DAGUERREOTYPE PLATES. 



Several plans have been suggested for accomplishing this much 

 desired object ; none, however, seem so well adapted as the follow- 

 ing, recently patented by M. Claudet, to whom the art is already 

 much indebted. In the specification, the process is explained as 

 follows : 



The process is established upon the following facts, which have 

 come to the knowledge of the inventor : 



1. A mixed acid, composed of water, nitric acid, nitrate of pot- 

 assa, and common salt, in certain proportions, being poured upon a 

 Daguerrotype picture attacks the pure silver, forming a chloride ot 

 that metal, and does not affect the white parts, which are produced 

 by the mercury ; but this action does not continue long. Then, by 

 a treatment with ammonia (ammonia containing already chloride of 

 silver in solution is preferable for this operation), the chloride of 

 silver is dissolved, and washed off, and the metal being again in its 

 naked state, or cleansed from the chloride, it can be attacked afresh 

 by the same acid. This acid acts better warm than cold. 



2 As all metallic surfaces are soon covered, when exposed to the 

 atmosphere, with greasy or resinous matters, it is necessary, in order 

 that the action of the acid upon the pure silver should have its full 

 effect, for the surface to be perfectly purified ; this is effected by 

 the employment of alcohol and caustic potash. 



3. When a Daguerrotype picture is submitted to the effect of a 

 boiling concentrated solution of caustic potash, before being attacked 

 by the acid, the state of its surface is so modified that the acid 

 spares or leaves, in the parts which it attacks, a great number of 

 points, which form the grain of the engraving. 



4. When the effect of the acid is not sufficient, or in other words, 

 if it has not bitten deep enough, the effect is increased by the fol- 

 lowing process : Ink the plate as copper-plate printers do, but 

 with a siccative ink ; when the ink is sufficiently dry, polish the 

 white parts of the plate, and gild it by the electrotype process ; 

 then wash it with warm caustic potash, and bite in with an acid, 

 which will not attack the gold, but only the metal in those parts 

 which, having been protected by the ink, have not received the 

 coating of gold. By these means the engraving is completed, as 

 by the action of the acid alone it is not generally bitten in deep 

 enough. 



