Thank you
Sent from my iPhone
On Feb 27, 2019, at 11:22 PM, `Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:============================================================================================================To
There is a fairly good short article on the wet plate process at:
https://en.wikipedia.org/wiki/Collodion_process
Wet plates or Collodion was invented by Fredrick Scott Archer about 1851
and slowly replaced the Daguerreotype. Wet plate was itself replaced by dry
plates using a gelatin emulsion about 1880. About 1890 silver-gelatin
emulsion coated on flexible film began to supplant glass plates but never did
entirely. The great dimensional stability of glass keep them in use for a
number of purposes. Curiously enough the cellulose nitrate used for the first
flexible film support is similar to the collodion used for the sensitive
coating on wet plates. Flexible film made motion pictures and small still
cameras possible.
https://en.wikipedia.org/wiki/Photographic_film
The collodion process continued to be used in the reprographic industry for
making half tone plates for many years after dry plates for the purpose
became available. Collodion has the advantage of extremely fine grain and can
be made to have extreme contrast which were useful properties for the process
as is the ability to strip the image layer off the glass after processing and
transfer it to the printing plate.
A good pamphlet about the half tone process is at:
https://www.getty.edu/conservation/publications_resources/pdf_publications/pdf/atlas_halftone.pdf
Eventually, self-screening films and plates were devised which did away
with the need for the difficult and dangerous wet plate process and also with
the delicate and expensive cross-screens required.
There are many experimenting with old processes now including collodion
and much literature is available both in print and on the web.
As a side note, one finds in fiction the idea that photographers commonly
had cyanide available in the darkroom. This is only partly true. Potassium
cyanide is a very effective solvent for silver. It is the basis of a
"reducer" (that word has another use in photography, developers are reducers)
a solution that removes some silver. A combination of iodine and cyanide
works well for removing dark spots on negatives or prints but ammonium
thiosulfate (rapid fixer) works nearly as well as cyanide and is not
dangerous. In making half tone plates on collodion a special reducer called
Monckhoven's reducer is used because it is both a reducer and intensifier at
the same time. It is used to sharpen up the dots on the plate but is
extremely poisonous because it contains both potassium cyanide and mercuric
chloride, two of the most toxic chemicals around. It was never found in
ordinary pictorial darkrooms but was convenient for detective story writers.
Potassium cyanide was also used as a fixing agent for the early collodion
process but much safer substances were found.
On 2/27/2019 9:28 PM, Dave Hornford wrote:
Eric
Can you refer me to something I can read about dry, or wet, plates. I may
wander into a patch of time for experimenting in the near future.
Sent from my iPhone
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
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