1855.] on Nature-Printing. 113 



He afterwards stated that he abandoned the process of electro- 

 typing in consequence of his finding it tedious, troublesome, and 

 costly, to produce large plates. Having occasion, however, to get 

 an article cast in brass, he was astonished at the beautiful manner in 

 which the form of the model was reproduced in the metal. He 

 determined, therefore, to have a cast taken in brass from a gutta- 

 percha mould of ferns, and was much gratified to see the impression 

 rendered almost as minutely as by the electrotype process ;* but, 

 however curious his individual specimens, the process produced no 

 practical result. 



In 1849, Professor Leydolt, of the Imperial Polytechnic Insti- 

 tute at Vienna, availed himself of the resources of the Imperial 

 Printing-OfHce to carry into execution a new method he had 

 conceived of representing agates and other quartzoze minerals in 

 a manner true to nature. Professor Leydolt had occupied himself 

 for a considerable period in examining the origin and composition 

 of these interesting objects in geology. In the course of his ex- 

 periments and investigations he had occasion to expose them to the 

 action of fluoric acid, when he found, in the case of an agate, that 

 many of the concentric scales were totally unchanged, while others, 

 to a great extent, decomposed by the acid, appeared as hollows 

 between the unaltered scales. It occurred to Leydolt that the 

 surfaces of bodies thus corroded might be printed from, and copies 

 multiplied with the greatest facility. 



The simplest mode for obtaining printed copies is to take an 

 impression direct from the stone itself. The surface after having 

 been etched is well washed with dilute hydrochloric acid and dried ; 

 then carefully blackened with printer's ink. By placing a leaf of 

 paperf upon it, and by pressing it down upon every portion of the 

 etched or corroded surface with a burnisher, an impression is ob- 

 tained, representing the crystallised rhomboidal quartz black, and the 

 weaker parts that have been decomposed by the action of the acid 

 white. It requires but a small quantity of ink — and particular care 

 must be exercised in the rubbing down of the impression. This 

 mode is good as far as it goes — but it is slow and uncertain — and 

 incurring a certain amount of risk, owing to the brittle nature of 

 the object ; and the effect produced is not altogether correct, since 

 it represents those portions black that should be white, and those 

 white that should be black. 



The stone is not sufficiently strong to be subjected to the action 

 of a printing-press ; an exact fac'simile cast, therefore, of it must 

 be obtained, and in such a form as can be printed from. To effect 

 this, the surface of any such stone (previously etched by corrosion) 

 must be extended by imbedding it in any plastic composition that 



♦ The casting in brass is a very interesting experiment — but its results 

 cannot be compared with the production of the electrotype. 



t India-paprr and Chalk-paper are the l)est adapted for the purpose. 



i2 



