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Lloyd Godman
Alternative
Photographic Processes - (Hand
made photographic -emulsions and processes)
Van Dyke Brown Prints - Historical context
Photographers have worked with the brown print photographic process,
in one form or another, for more than 100 years. In the typical historical
description of making brown prints, the process involves a ferric ammonium
citrate sensitizer (agent to respond to light) that is mixed with a
silver nitrate solution (agent that forms the final image). When the
two chemicals are coated on paper and exposed to sun light under a negative,
the ferric compound turns ferrous, producing a quite visible image in
iron. In brown printing, water is used not only to develop the brown
print image but also to fix it and wash away the non-image-forming chemicals.
The process is one of three alternative photographic methods that rely
on the photo-reduction of ferric ions rather than silver ions. (Cyanotype
and palladium processes are the other two.) Van Dyke Brown prints have
a beautiful rich brown colour with subtle gradations in tonality. Unfortunately,
they are also fairly fragile and ephemeral in that they can fade with
continued exposure to high levels of ultra violet light.
Because the silver salts used in the sensitiser merge into the base
material, rather than sitting on the surface as with conventional photographic
materials, the image can appear to be dyed into the base material.
Most
historians agree that the brown print process originated in the researches
of J.F.W.Herschel around 1840, who is credited as being the first to
form an image with an iron sensitizer. Many of these experiments remained
little more than laboratory curiosities for about 50 years. Since about
1890, workers and writers have consistently viewed the brown print as
a version of the kallitype for around this time it found some flavor
for making contact prints. The van Dyke Brown was devised by W J Nichol
in 1899, based on the Kallitype process of Sir John Herschel in the
1840s.
Most
historians agree that the brown print process originated in the researches
of J.F.W.Herschel around 1840, who is credited as being the first to
form an image with an iron sensitiser. He is recognized as inventing
a similar process called the argentotype in 1842. While the process
of making an argentotype differs slightly from the those of making a
van Dyke print, the chemistry of the two are essentially the same. Both
utilize the photosensitivity of iron salts as well as the ability of
ferrous ions [iron(II)] to reduce silver ions to silver metal. (As in
the cyanotype process, the photo active component in the sensitised
paper for a van Dyke brown print is an iron(III) salt of an organic
acid. The result of Herschel's process was a print that looked a bit
like the prints that Fox Talbot made from his salted paper. Many of
these experiments remained little more than laboratory curiosities unsuitable
as resolved photographic processes for about 50 years. Since 1890, photo-workers
and writers have consistently viewed the brown print as a version of
the argentotype for around this time it found some flavor for making
contact prints. . There seems to be some confusion about the name in
some manuals where states that the VanDyke is miss-named as Kallitype,
while Dick Stevens description of it as a Kallitype process in his book
"Making Kallitypes", separates the two, he sees them as related
and refers to it as a similar process as brown print Kallitype.
Argentotype
The
Argentotype In Herschel's process, the argentotype, the paper, which
was coated with a solution of ferric ammonium citrate was exposed to
light. The exposed paper, with its unstable image, was placed in a bath
containing silver nitrate to produce the second reaction, the one depositing
the small bits of silver that make up the final image. The paper was
soaked in a fixer solution to remove excess silver ions and rinsed thoroughly
before drying. The van Dyke brown process is a refinement of Herschel's
process, and uses paper that is coated with a solution containing both
ferric ammonium oxalate and silver nitrate. Upon exposure some of the
ferric ions in the sensitised paper are reduced to ferrous ions, but
the second redox reaction (silver ions to silver) occurs only after
the exposure and when the paper is put in water. If the exposed paper
(with a visible image) is placed in the fixer bath before it is placed
in a water bath, the image will disappear.
The
Name
Van
Dyke Brown in Painting:
The
name Van Dyke brown is actually attributed to pigments used in painting.
This is a transparent brown pigment containing usually over 90% of organic
matter.
It
is pronunced: van dike braoon.
Some
alternative names as follows: Cassel earth, Cologne earth. Non-English
names: · German: Kasseler Erde, Kölnische Erde ·
French: terre de Cologne, terre de Cassel · Italian: terre de
Cologne, terre de Cassel Chemical name: Derived from humic substances
Still in use today, Van Dyke brown pigment has been positively identified
in paintings since 17th century and may have been discovered about late
16th or early 17th century.
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