THE 
POPULAR SCIENCE REVIEW. 
PHOTOGRAPHIC PRINTING AND ENGRAVING. 
BY WILLIAM CROOKES, F.R.S. 
HE uncertainty which is a necessary accompaniment of 
the ordinary method of photographic printing, its great 
expense, the extreme difficulty of producing a sufficient 
number of presentable pictures of the same subject to satisfy 
the requirements of book-illustration, and the utter impossi- 
bility, in the present state of our knowledge, of producing a 
photographic print which can be relied upon for permanency, 
have caused men of science, from the earliest days of photo- 
graphy, to turn their attention to the problem of causing the 
photograph to impress itself on a metal plate or lithographic 
stone in such a manner that the subsequent copies could be 
struck off in printer’s ink. 
A somewhat similar problem, but one of far less utility, has 
been to produce photographic prints on paper prepared in 
such a manner that the dark portions of the image shall be 
composed of carbon, or some other body of which it can con- 
fidently be asserted that no ordinary atmospheric influences 
would cause it to change. This latter problem has been 
followed up with some ingenuity by many experimentalists, 
both in England and on the Continent ; but as they are all 
open to the grave objection that the mechanical operation 
of printing is as slow and uncertain as the ordinary process, 
they need not be further alluded to. 
Passing rapidly over the first crude attempts of Donne, 
Niepce, Berres, Eizeau, Negre, and perhaps some others, 
none of which met with much success, we come to the plioto- 
glyphic process of Mr. Talbot, the basis of which was first 
published in the early part of 1853. The principle which 
he adopted was an entirely new one in that branch of 
the art ; it may be briefly explained as follows : — A solution 
of gelatine or isinglass, containing a little bichromate of 
vol. hi. — NO. IX. B 
