21 



5. To protect the plate from the effects of wear, produced by 

 the operation of printing, the following process is employed : The 

 surface of the plate is covered with a very thin coating of copper, 

 by means of the electrotype process, before submitting it to the 

 operation of printing ; and when that pellicle or coating of copper 

 begins to show signs of wear, it must be removed altogether, by 

 plunging the plate in ammonia, or in a weak acid which, by electro 

 chemical action, will dissolve the copper, without affecting the 

 metal under it ; the plate is then coppered again, by the same 

 mean*, and is then ready for producing a further number of im- 

 pressions. This re-coating operation may be repeated as many 

 times as may be required. The-following is the description of the 

 whole process, which is divided into two parts, consisting of a pre- 

 paratory and finishing process : 



Preparatory Engraving. For this operation, which is the most 

 delicate, it is necessary to have, 1 . A. saturated solution of caustic 

 potash. 2. Pure nitric acid at 36 of the areometer of Beaume 

 (spec. grav. 1 '333.) 3. A solution of nitrite of potassa, composed 

 of 100 parts of water and 5 parts of nitrite, by weight. 4. A solu- 

 tion of common salt, composed of water 100 parts, and salt 10 

 parts, by weight. 5. A weak solution of ammoniacal chloride of 

 silver, with an excess of ammonia. The ammoniacal chloride of 

 silver must be diluted with 15 or 20 parts of pure water. In the 

 description of the process, this solution will be called ammoniacal 

 chloride of silver. 6. A weak solution of ammonia, containing 4 or 

 5 thousandths of liquid ammonia. This solution will be called 

 ammoniacal water. 7. A weak solution of caustic potash, contain- 

 ing 4 or 5 thousandths of the saturated solution, which will be 

 called alkaline water. 8. A solution composed of water 4 parts, 

 saturated solution of potash 2 parts, alcohol 1 part, all in volume. 

 This solution will be called alcoholized potash. 9. Acidulated water, 

 composed of water 100 part?, and nitric acid 2 parts, in volume. 

 Besides, it is necessary to have three capsulze or dishes, made of 

 porcelain, large enough to contain the plate, and covered with an 

 air-tight piece of ground plate-glass, and two or three more capsulse 

 which do not require to be covered ; two or three glass funnels, to 

 wash the plate ; and two or three glass holders, in the shape of a 

 spoon or shovel, by which the plate is supported when put in and 

 taken out of the solution, without touching it with the fingers. 



The Daguerrotype plate is submitted to the engraving process, 

 after having been washed in the hyposulphite of soda, and after- 

 wards in distilled water. 



