152 
POPULAR SCIENCE REVIEW. 
“ relief-printing 33 — owes its origin. It is only in relief, how- 
ever, for a very short time, for as it dries this peculiarity dis- 
appears, nntil, when it has become quite dry, no trace of 
relief is apparent. From the fact that the print must 
remain in the press for nearly a minute ere it is ready for 
removal, it is expedient that one operator should have several 
presses to work so as to fill up his time. By adopting this 
plan a skilled printer will be enabled to produce prints at the 
rate of from 150 to 200 per hour. 
To prevent the print from sustaining any damage from 
moisture, gelatine being readily susceptible to hygrometric 
influences, the prints before being mounted are fixed, — an 
operation performed in a very simple manner, viz., by im- 
mersing them for a short time in a solution of alum. By this 
means the image is rendered insoluble, so that when it is 
again dried it is found to be impervious to moisture, and its 
mechanical condition, too, is improved. 
The cost of photographs printed in the manner described is 
very moderate. The ink and paper combined will not amount 
to a farthing, each print of a size suitable for average book 
illustration, and all the waste ink recovered from the super- 
fluity around the edges of the mould may be instantaneously 
utilised by being again returned to the vessel from which the 
warm and melted ink is poured ; and thus the economy of the 
process is in no way affected by the quantity of ink that may 
be poured on to the surface of the plate during the operation 
of printing. 
From what has been said it will have been seen that Mr. 
Woodbury, in the process described, has introduced an entirely 
new principle in printing — a principle by which the most 
perfect gradation is obtained, differing in this respect from 
any other kind of press-printing. When a suitable paper is 
employed to receive the image, details almost microscopic in 
their minuteness are found in the finished picture, and this 
combined with brilliance and vigour. If the impressions be 
received on a plate of opal glass instead of on paper, transpa- 
rencies of the richest and most delicate nature are obtained, 
rivalling the choicest productions of Ferier and Soulier. 
