412
of silver nitrate to silver by a reagent in the developing
solution; the silver is then deposited on the latent image
serving as a framework for image formation.
Physical development was the predominant manner
of developing in the early days of photography—a peri-
od spanning 1839–1862. During this time, it was mostly
used for negative-making purposes, although a few
photographers in the 1850s, like Louis-Désiré Blanc-
quart-Évrard and Thomas Sutton, also used it to make
positive prints from negatives. Signifi cant photographic
processes that utilized physical development during
the period included the calotype process (beginning
1839–1840), the albumen process (beginning 1848), the
wet-collodion process (beginning 1850–1851), and the
waxed-paper negative process (beginning 1851). Sig-
nifi cant reagents used in physical development during
the period included gallic acid (beginning 1839–1840),
ferrous sulfate (beginning 1844), and pyrogallic acid
(beginning 1850–1851).
For a photographic image to be formed by physical
development at the time, there needed to be an excess of
silver nitrate in proportion to the halide used to make the
light-sensitive surface; otherwise, the operation would
not have succeeded due to a lack of oxidizing material.
Mid-nineteenth century photographers obtained an
excess of silver nitrate in one of two ways: either they
could leave excess silver nitrate in the sensitive surface
being formed (which necessitated an immediate expo-
sure and development while the negative was still damp
due to the oxidizing tendency of the silver nitrate) or
they could rinse the sensitized negative in water (thus
removing excess silver nitrate), dry it for exposure at
a later date, and then reintroduce excess silver nitrate
to the developing solution just prior to development.
The former “wet” method predominated with calotype
and early wet-collodion photography (1839–1862);
it continued to be used with wet-collodion until the
1880s, due to its familiarity and the relative brevity of
exposure times that were obtained with it. The latter
“dry” method was confi ned to the dry, waxed-paper
negative and dry-collodion processes (1851–1862).
While convenient for the voyager, the dry processes
suffered from one major drawback when coupled with
physical development: exposures were much longer than
with the wet processes.
With physical development, the developing solution
needed to be acidic or neutral, rather than alkaline, in
order to prevent a spontaneous reduction of the excess
silver nitrate to silver, which would have blackened
the image entirely. This being the norm, there were a
few noteworthy exceptions. In 1851, two French pho-
tographers, the abbé Léon-Emmanuel-Simon-Joseph
Laborde and Baron Louis-Adolphe Humbert de Molard,
succeeded in reducing exposure and development times
by adding trace amounts of acetates to developing solu-
tions, making them mildly alkaline. In 1856, an English
photographer, W.D. Parr, added sodium acetate to a
preliminary iodizing solution, causing it to function as
a built-in accelerator. The success of these experimental
methods was limited, and their unreliability (given the
excess silver nitrate in solution) prevented them from
being fully adopted.DEVELOPING
Henneman. The Reading
Establishment.
The Metropolitan Museum of Art,
Gilman Collection, Gitft of The
Howard Gilman Foundation, 2005
[2005.100.171ab(b)] Image © The
Metropolitan Museum of Art.