214 ELECTRO-M ET ALLURGY 



For tho multiplication of engraved copper-plates, tho electrotype process has boon 

 very extensively adopted. A reverse of the plate is first obtained by tho deposition of 

 copper; this serves as a mould, from which many copies of tho original plate are ob- 

 tained by depositing copper upon it, and then separating tho two. The mode practised 

 by the Duke of Leuchtenborg is to print from an engraved plate on very thin paper 

 with a mixture of resin of Damara, rod oxide of iron, and essence of turpentine. While 

 the impression is wet, the paper face downwards is pressed upon a polished plato of 

 copper. When dry tho paper is washed away, and tho impression remains. AM 

 electrotype copy from this is obtained in intaglio, and is fit for tho uso of the printer. 



Galvanography is a picture drawn originally in varnish on tho smooth plate, and 

 then treated in a similar way to the above. 



The plates on rollers used by calico printers have been multiplied like engraved 

 plates. 



Glyptography is a name given by Mr. Palmer to his process. Ho blackens a fair 

 copper-plate with sulphurot cf potassium, covering it uniformly with a coating of wax 

 and other things, then draws the design through the wax with fine tools. From tho 

 plate thus prepared, an electrotype is taken in tho usual way, and is backed up and 

 mounted as an electro-glyphic cast to print from as from a wood-block. For a stcrco- 

 glyphic cast to work from as a stereotype-plate, a plaster copy is taken of the original 

 drawing, the high lights are cut out, and then an electrotype copy is made. 



Electro-tint is done by drawing with wax or varnish any design on a fair copper- 

 plate, and making an electrotype copy for the printer's use. 



Fern-leaves, &c., are copied by being laid on a sheet of soft gutta-percha, pressed 

 into the surface by a smooth plate to which pressure is applied, and then removed in 

 order to subject the gutta-percha mould to the electrotype process. This is NATURE 

 PBINTING, which see. 



MM. Auer and Worring have copied lace, embroidery, flowers, leaves of trees, en- 

 tire plants, fossils, insects, &c., in their natural relief, by laying the objects upon a 

 plate of copper, after having soaked them in spirits of wine and turpentine so as to fix 

 them. A plate of clean lead is laid over, and, on being pressed, an intaglio copy is 

 produced on it of the object. From this an electrotype is obtained. 



Undercut medallions, &c., are copied in elastic moulds made of treacle and glue 

 in the proportions of 1 to 4. Masks and busts may also be obtained in such moulds. 



Electro-cloth was made by saturating the fibre of canvas or felt, making it con- 

 ducteous in the usual way ; it was proposed in place of tarpaulins as a water-tight 

 cover. 



Retorts and crucibles, &c., of glass or porcelain, have been successfully coated 

 with electrotype copper by first varnishing or otherwise preparing the surface to retain 

 the black-lead, and then treating them as usual. 



Soldering copper surfaces has been accomplished by galvanic agency. Tho ends 

 to bo united are placed together in the solution of sulphate of copper, and connected 

 with the battery as for ordinary deposition. Parts not included in tho process aro 

 protected off by varnish ; copper is then deposited, so as to unite tho separate pieces 

 into one. 



Iron may be coated with copper. But hero a new feature comes into view. 

 Sulphuric acid leaves the copper of the sulphate, combines with iron, and deposits 

 copper on its surface without the aid of tho voltaic apparatus. Tho iron surface is 

 imperfectly covered with copper, and no firm perfect deposit occurs. In order to obtain 

 solid deposits of copper on iron, it is necessary to use a solution that has no ordinary 

 chemical reaction upon iron. Cyanide of copper is used, which may bo obtained l>y 

 dissolving sulphate of copper in cyanide of potassium. This solution requires to be 

 raised to and retained at a temperature not greatly below 200, in order to give good 

 results. 



Electro-zincing is applied to surfaces of iron, in order to protect them from cor- 

 rosion. A solution is made of sulphate of zinc, which is placed in a trough ~R,fig. 794. 

 Two or three battery colls are required. Tho iron to bo zinced is connected with tho 

 zinc end of the battery, and a plato of zinc with tho copper end. 



Voltaic brass does not appear to have boon obtained in a solid distinct form, but 

 has been successfully produced as a coating upon a copper surface. Separate solutions 

 are made of sulphate of copper and of sulphate of zinc in cyanide of potassium. Tho 

 two solutions aro then mixed, and placed in a decomposing trough. Two or three cells 

 of a battery are used, and a brass plato connected with tho copper end. An electrotype 

 copper medal or other prepared surface is connected with tho zinc. Brilliant and \< <-r- 

 fect brass soon appears, and will deposit slowly for some hours ; but after a while, tho 

 character of tho solution changes, and copper appears in place of brass. 



This hasty glance at tho leading applications of this art will give an idea of its 

 utility. It also comes into play in cases where least suspected, fins were tinned by 



