[pure-silver] Re: what causes pinholes in emulsion?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 20 Feb 2009 14:53:36 -0800
----- Original Message -----
From: "Shannon Stoney" <shannonstoney@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, February 20, 2009 11:32 AM
Subject: [pure-silver] what causes pinholes in emulsion?
I am printing some film that I shot over a year ago, and
there are lots of pinholes in the emulsion. At first I
thought it was the brand of film, and one roll did seem
worse than the others: the Bergger roll. But the problem
is on the FP4+ negatives too. Maybe it was something in
my processing that day? I seem to remember that if the
temperature difference between the developer and stop is
too much, like if the developer is warm and the stop is
really cold, it can happen. Is that right?
--shannon
Pinholes are nearly always a manufacturing problem,
check to see if there are actual voids in the emulsion or if
there is something else there. An example is dust on the
negative during esposure which can leave clear spots which
mimic pinholes. Incompletely dissolved chemicals in
developer mixed from powder can do the same as can dirt in
the developer. The particals are deposited on the surface
and prevent full development. Sometimes even rapid agitation
will not dislodge them. Air bells, i.e., bubbles formed on
the surface of the emulsion during development can also
mimic pinholes although air-bells are generally larger and
often have a dark ring around the clear spot.
The problem of bubbles of gas forming in the stop bath
and causing disruptions of the emulsion is extremely rare,
for one thing, this outgassing takes place only in
developers containing carbonates, few current film
developers have them. Developers like D-76 (with Borax) or
Xtol (metaborate) do not outgas.
Further, modern emulsions are very hard, most B&W
emulsions are hardened about the same as color film, that
is, to take 100F processing temperatures. In the past,
meaning in the 1920s to about the late 1930s, emulsions were
much softer and sometimes pinholes would form due to gas
bubbles forming.
Generally, temperature differences between baths have
little effect on modern films for the same reason as stated
above. In any case, the results would be softening of the
emulsion by hot solutions with attendant swelling and sudden
shrinking when placed in the cold solution causing
reticulation, i.e., fine wrinkles, in the emulsion. This has
a very characteristic look and is not the same as pinholes.
I have never heard of pinholes being formed by temperature
diffences. Reticulation is sometimes done delibrately as a
special effect but is very hard to accomplish with modern
film.
I have also never heard of pinholes being formed due to
film age.
Since you are getting the same effect with more than
one brand of film I would be much more suspicious of dirty
developer pr dirt in the tank than anything else. First step
is to wash the equipment very thoroughly and second step is
to filter the processing solutions. Coffee filters work OK
for this and are cheap. See if your tap water is dirty. If
it is try boiling it and then filtering it through a Brita
filter. This will remove particulate matter, drive off
dissolved gasses and coagulate and remove any organic matter
(bits of tree root) in the water. It will also remove some
types of "hardness". A three minute rapid boil followed by
allowing the water to stand until cool will do. Decant the
clear water and run it through the Brita or similar filter
to remove stuff that boiling does not remove. Such treatment
is probablly not necessary but some areas have bad water
that needs it. At the least filter the water you use for
photographic purposes through a coffee filter.
Also, vacuum out your camera or cameras.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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