210 ANNUAL OF SCIENTIFIC DISCOVEEY. 







the drawing and the surface of the stone are destroyed. The unalterability 

 of the drawing by the preparation is a very remarkable feature in this species 

 of engraving, for after its application the drawing remains exactly the same 

 as when it came from the artist's hand. The plate thus prepared with the 

 gall nut decoction and afterwards gummed, is then immediately cleared of the 

 gum with water, and I wash the drawing with essence of turpentine. In this 

 state, scarcely anything is visible on the plate ; but every part of the drawing 

 has a strong affinity for greasy substances, and all the other parts of the plate 

 repel them. If one wished to print lithographically, it would be sufficient to 

 damp the plate and pass a roller over it charged with printing ink, in order 

 to obtain proofs. By my process of engraving, instead of printing ink, I 

 apply in the same manner, by means of a roller, a varnish which, on account 

 of the different affinities of the plate, perfectly replaces the chalk or draughts- 

 man's ink, and is as easily applied as printing ink upon a lithographic draw- 

 ing, and it takes up no more time to lay on the varnish than to pull a litho- 

 graphic proof. This varnish is composed of asphaltum, of linseed oil boiled 

 with litharge, and of essence of turpentine. When the varnish is dry. the 

 plate of zinc is placed in metallic connexion with a copper plate of equal 

 size. Over the plate which has the drawing a very weak solution of sulphuricf 

 acid is passed with a brush in order to cleanse it, and the two plates are then 

 plunged horizontally and facing each other, at a distance of five millimetres 

 (somewhere about inch), into a solution of sulphate of copper of fifteen 

 degrees. The sulphuric acid from the decomposition of the sulphate of 

 copper dissolves all the parts of the zinc plates which are not covered by the 

 varnish, and this substance not being decomposed by contact with the 

 sulphate of copper, does not experience the least alteration. On account of 

 the great affinity which the sulphuric acid has for the zinc, in comparison 

 with the slight affinity which it has for the copper, the employment of this 

 salt and the approximation of the plates give rise to a very energetic electro- 

 chemical action, and at the end of a few minutes the plate is engraved. 

 During the operation the zinc plate is frequently withdrawn and washed with 

 pure water, in order to get rid of the parts of the sulphate of zinc and of me- 

 tallic copper which adhere to its surface. To prove the unalterability of my 

 varnish, you may make a drawing on a porcelain plate and fill it with the 

 solution of the sulphate of copper: the drawing will undergo no change. 

 The voltaic pile has for some time been employed to engrave on copper, but 

 no one before I made the experiment has attempted relief-engraving by 

 electro-chemical means. Nevertheless, it has often been observed that by the 

 aid of electricity very deep lines could be cut in copper plates without 

 widening the strokes, for while the chemical action alone bites on all sides, 

 an energetic electro-chemical action only takes effect on the depth. This 

 superiority of galvanic electricity over the simple action of acids renders 

 possible that kind of engraving in relief which requires great depth." 



After recognising the assistance rendered to this new invention by the pro- 

 cesses of lithography and the science of electro-metallurgy, M. Devincenzi 

 goes on to illustrate its importance. This is chiefly shown by the facilities 

 which it offers for producing, like ordinary types, an almost unlimited number 



