PROCESS OF ELECTRO- GILDING. 



129 



the less battery power is required: generally three or four pair 

 of plates are used for gilding, and the solution is kept at 130 

 to 150 Fah. ; but one pair will answer if the solution is heated to 

 200 P . 



Process of Gilding. As the process of gilding is generally per- 

 formed upon silver articles, the previous immersion in nitric acid 

 is unnecessary. The method of proceeding is as follows : When 

 the articles are cleaned, as described in our chapter on plating, they 

 are weighed and well scratched with wire brushes, which cleanse 

 away any tarnish from the surface, and prevents the formation of 

 air- bubbles ; thev are then kept in clean water until it is convenient 

 to immerse them in the gold solution. One immersion is then 

 given, which merely imparts a blush of gold ; they are taken out 

 and again brushed ; they are then put back into the solution, and 

 kept there for three or four minutes, which will be sufficient if the 

 solution and battery are in good condition ; but the length of time 

 necessarily depends on these two conditions. 



Iron, tin, and lead are very difficult to gild direct ; they therefore 

 generally have a thin coating of copper deposited upon them by the 

 cyanide of copper solution, after which they must be immediately 

 put into the gilding solution. 



Conditions required in Gilding. The gilding solution generally 



contains from one-half to an ounce of gold in the gallon, but for 

 covering small articles, such as medals, for tingeing daguerreotypes, 

 gilding rings, thimbles, &c., a weaker solution will do. The solu- 

 tion should be sufficient in quantity to gild the articles at once, so 

 that it should not have to be done bit by bit ; for when there is a 

 part in the solution and a part out, there will generally be a line 

 mark at the point touching the surface of the solution. The rapidity 

 with which metals are acted upon at the surface line of the solution 

 is remarkable. If the positive electrode is not wholly immersed in 

 the solution, it will, in a short time, be cut through at the edge of 

 the water, as if cut by a knife. This is also the case in silver, cop- 

 per, and other solutions, as before referred to. 



maintaining the Gold Solution. As the gold solution evaporates 

 by being hot, distilled water must from time to time be added : the 

 water should always be added when the operation of gilding is over, 

 not when it is about to be commenced, or the solution will not 

 give so satisfactory a result. When the gilding operation is con- 

 tinued successively for several days, the water should be added at 

 night. The average cost of depositing gold is about 2d. per penny- 

 weight. 



The means of testing the free cyanide of potassium, as described 

 for silver, is not applicable to the gold solution. To obtain a deposit 



