HISTORY OF BOTANIC ILLUSTRATION. 
155 
roller, which inks the more delicate parts, and it is then pulled 
on ordinary printing-paper. The film thus takes a gradated 
amount of ink, corresponding to the negative. There is one 
drawback to this effective and beautiful process, and that is, no 
dependence can he placed on the durability of the film, which 
may break np in the press, almost without notice ; consequently 
the workman is obliged to have a second film in reserve, in case 
the first one gives way; another inconvenience is the length of 
time the collotype ink takes to dry on the paper. The samples 
shown are of dried specimens of gentians, a garden variety of 
a flowering shrub, and Salvia leaves (PI. Ill, fig. 4) ; the latter 
displays a pseudoscopic effect on being turned upside down, as 
though the under sides of the leaves were shown. 
The last process which I have to describe is that known as 
Woodbury type, from the name of its inventor. The method is 
practically the Same as it was left at his death. It represents the 
object with the minutest detail absolutely without grain of any 
kind. A thick film of gelatine and bichromate is exposed under 
a negative, and washed free from unused portions, and when dry 
it is practically incompressible. It is then placed in a steel box 
with a thick plate of lead above it, and pressure of about two tons 
to the inch is applied, as in the previously-described Bradbury’s 
Nature Printing. This lead forms the matrix for printing. It 
is placed on a press with a hinged lid of glass, and the face of 
the lead being slightly oiled, a small amount of warm gelatine, 
tinted as required, is poured on it, paper placed upon it, and the 
lid shut down. In a few minutes the fluid gelatine has set, and 
on opening the mould the sheet of paper turns out with the 
coating of impressed coloured gelatine, which, after immersion 
in a bath of alum to render it permanent, has to be dried and 
trimmed to form the perfect print. The original gelatine is quite 
unharmed by the heavy pressure, and can be used repeatedly for 
new lead matrices. Owing to the slow printing, and every print 
having to be mounted, the cost is almost prohibitive for plates 
of botanic subjects. I have no slide to represent this process, but 
I place on the table prints from the same negative, showing the 
difference between Collotype and Woodbury type. 
I have only given a very brief outline of the modern processes, 
for they are so varied by different practitioners that I cannot 
pretend to describe all the modifications employed. I have en¬ 
deavoured to explain how the modern blocks are made, at all events 
in the main methods used, and, though necessarily brief, I trust 
I have made the processes intelligible. 
