A Manual Of Photography
Forfatter: Robert Hunt
År: 1853
Forlag: John Joseph Griffin & Co.
Sted: London
Udgave: 3
Sider: 370
UDK: 77.02 Hun
Third Edition, Enlarged
Illustrated by Numerous Engrabings
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252
PRACTICE OE PHOTOGRAPHY.
or two, of great force. When this effect is produced, the liquid
should he poured off, and the plate washed and dried.
“ In this operation the silver is dissolved, and
the gold precipitated upon the silver and mercury,
hut with very different results: in effect, the su-
ver, which, by its reflection, forms the shades of
the picture, is in some way darkened by the thin
film of gold which covers it, from which results
a strengthening of all the dark parts. The mer-
cury, on the contrary, which, in the state of an
infinite numherof small globules, forms the lights,
is augmented in its solidity and brightness by its
64.
union with the gold, from which results a great
degree of permanency, and a remarkable increase
in the lights of the picture.
The plates are then washed by means of an arrangement of
this order. The apparatus represented in fig. 65 may be employed.
« is a vessel sufficiently large to take the
plate, and not more than half an inch
wide: this is filled with distilled water,
which is heated by means of a spirit-lamp;
6 is a stand supporting the trough, and c
a holder for the plate. After the plate
has been immersed for a few minutes,
it is to be drawn out slowly, and by
blowing on it the water is removed, and
the warm metal rapidly dried, buch are
the principal processes which have been
adopted in the daguerreotype manipu-
lation. Other modes for giving perma-
nency to the daguerrean image have been adopted, but none of
them have been so thoroughly successful.
It appears advantageous to quote a few of the modified forms
of proceeding for fixing these pictures, when obtained, which
have from time to time been recommended.
Extract of a Letter from .1/. Preschot to 3I. Arago.
In one of the sittings of last month you mentioned a process
for fixing photogenic images on metal. Knowing, as 1 do, the
interest you take in the beautiful discovery of the daguerreotype,
I hope you will excuse the liberty I take in troubling you witi
results which I obtained in experiments made a few months ago.
Photogenic images, obtained by M. Daguerre s process, may
be fixed by treating them with a solution of hydrosulphate of
ammonia. ^For this purpose, a concentrated solution of this