104 J. Waterliouse — The Application of Fliotograpliy [No. 2, 



containing a mixture of 1 part chlorate of potash, 10 parts muriatic acid 

 and 48 parts water, and allowed to remain till the weakest lines of the 

 drawing begin to appear. It is then well washed and the asphaltum cover- 

 ing the lines is removed with benzole. The design will now be seen stand- 

 ing in a slight relief, and an electrotype must be made in order to obtain 

 a printing plate from which impressions may be taken in the ordinary way. 

 The sharpness of the lines is better preserved by making a relief and 

 electrotyping, than it would be by biting in. 



The best results by this process are obtained from subjects in line, and 

 even with these the operation of ' biting in' demands a little manipulative 

 skill. Good results have, however, been obtained in reproducing half-tone 

 subjects, but they require the greatest skill on the part of the manipulator 

 and generally much re-touching by a practised engraver. 



A modification of Niepce's process, by which good results have been 

 obtained, has been introduced by M. Negre, it is briefly as follows : 



A plate of steel is covered with a coating of bitumen or bichromated 

 gelatine and exposed to light under a negative. After development by a 

 suitable solvent, which removes the j)arts not acted on by light, the plate 

 is placed in a solution of gold and, by means of a galvanic battery, a thin 

 regular coating of gold is deposited on those parts which present a clean 

 metallic surface ; the remainder of the sensitive coating is then removed, 

 and a beautiful damascened design in gold is obtained. The gold adheres 

 well to the metal surface and as it is not attacked by the etching liquid, 

 the design may be etched without injuring the ground of the plate. 



This process also appears only suitable for line work, though it is said 

 that satisfactory results in half-tone have been obtained with it. 



M. Baldus, of Paris, is said to have used a similar process, but to have 

 etched his plates in a solution of sulphate of copper by attaching them 

 to the positive pole of a galvanic battery. 



The processes dependent on the use of asphaltum are all more or less 

 slow and uncertain in practice, and if not already quite abandoned in favour 

 of the quicker and more certain processes dependent on the use of gelatine 

 and bichromate of potash, are rapidly becoming so, especially as their use- 

 fulness is almost entirely confined to reproducing subjects in line. Exceed- 

 ingly fine results can, however, be produced in this manner, and it is 

 particularly valuable in eases where an ' etching' or ' biting in' process is 

 required, because the bitumen forms a much better ' resist' for the acid or 

 etching liquid than does gelatine, as we shall now see. 



EtcJdng processes with Gelatine. — In 1852, Mr. Henry Fox Talbot 

 brought forward a method of photographic engraving called ' Photoglypby,' 

 which is of some interest as being the first practical photographic process 

 founded on Ponton's discovery of the decomposition of bichromate of 



