Contact print papers

For Jim Cartwright, I was sure someone would write in about chloride
papers, but I guess no one did (unless I missed it.)  Chloride refers to
the halide salt of silver used in the light sensitive product.  The
halide used has a strong affect on the light sensitivity of the
material.  Silver Fluoride would never be used due to it's relatively
high solubility in water and also because it would be painfully slow.
Silver chloride is the slowest halide salt used in photography.  This is
one reason why historic printing-out papers (all chloride papers) had to
be exposed for minutes to hours to get an image.  However, chloride
papers are slow enough (even though you don't print-out the image
anymore) that they are good for contact printing. Bromide papers and
mixed "chloro-bromide" papers are the most popular papers for making
enlargements.  Finally iodides or mixtures of iodides and bromide are
used for camera films.  (It would be impractical to make an enlarging
paper that used exposures of 1/100 or 1/1000 sec under the enlarger.)
The other influence of halide source is the ease with which it can be
fixed.  Silver iodide is the least soluble and hardest to fix out, while
silver chloride is very easily fixed.  I have never seen anyone select a
halide based on solubility, however.

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                  Conservation DistList Instance 5:18
               Distributed: Wednesday, September 4, 1991
                        Message Id: cdl-5-18-005
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