[pure-silver] Re: Weird Film Issue
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 8 May 2012 10:57:02 -0700
----- Original Message -----
From: "BOB KISS" <bobkiss@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, May 08, 2012 5:06 AM
Subject: [pure-silver] Re: Weird Film Issue
DEAR RICHARD,
Please give us your take on this: I know that pin holes
occur from
the interaction of a carbonate (e.g. sodium) with acid,
like the acetic acid
stop bath, but I also thought that this we very
temperature dependent. When
using a developer-stop bath process, I have always
processed at 68-70 F and
have never experienced pin holes with the 8 different
films I have used over
the years. I mostly use PMK with a water rinse and this
is a non issue with
this dev but there are times I want the effect of other
devs.
I recall a student who said that I was being compulsive to
insist
that he process at 68-70 F using D-76 and stop bath. He
said he didn't want
to spend the time and money keeping his darkroom cool and
cooling the solns
before processing. He insisted that he could just adjust
the dev times and
process at 80 F or higher. Well, his rolls of 120 negs
looked like they had
been shot with birdshot...so many tiny clear holes, they
were all ruined. A
rather expensive lesson he will never forget.
CHEERS!
BOB
Most of what I know is conventional wisdom, here it is
FWIW:
Pinholes can be caused by gassing of the developer. It
appears that only carbonates react with acid to produce
carbon dioxide gas. This is the familiar reaction of
vinegar and baking soda or an Alka-Seltzer. Developers made
without carbonates do NOT produce any gas, these include
D-76, which is made with borax and developers containing
metaborates (Kodalk). There is some question in my mind if
even carbonate containing developers can cause pinholes in
modern hardened emulsions. I think this fear is a holdover
from the 1920s and 1930s when emulsions were very soft.
There are other causes for pinholes such as the deposition
of undissolved particles on the emulsion during development.
However, these cause tiny clear spots where true pinholes
are actual disruptions of the emulsion. Pinholes do not
seem to be a problem for prints even though most print
developers have carbonate in them. Probably, if they exist,
they are too small to be of significance.
Low temperatures are also a holdover from much earlier
times when emulsions were very soft. This may again be a
problem because many films are now made by small
manufacturers using very old technology. Until about 1940
(not an exact date) the standard processing temperature was
65F. Around then it was increased to 68F because most
emulsions were sufficiently hardened to withstand it. Some
modern emulsions are hardened enough to take 100F processing
but only some.
In the old days temperatures up to perhaps 75F were
considered normal but much above that, certainly at 80F, it
was advisable to use "tropical" processing with additions of
sodium sulfate in solutions and perhaps additional
hardening. I doubt if this is necessary with films made by
the major manufacturers, namely Kodak, Ilford, and Fuji, but
one should be careful of films made in the smaller plants.
I can't explain your students films but would be
interested in what film he used. This sounds more like
reticulation than pinholes. Reticulation is the wrinkling
of the emulsion caused by excessive softening and by loss of
the adhesion between it and the support. Reticulation was
very common in the bad old days and was the main problem
with high temperature processing. It is also the reason
that older books recommend that all solutions be at the same
temperature. Actually, reticulation is hard to produce on
modern films and may take extreme change of temperature for
success. I think the old advice about matching temperatures
within a couple of degrees was always exaggerated but
perhaps not.
Note that there are other effects that can cause
distortion of soft emulsions; simply the change in pH
between developer and acid stop bath or fixing bath will
cause mechanical stress. Again, this has not been a
significant problem for many decades.
Its probably safe to work up to about 75F with most
modern materials and some developers recommend the higher
temperatures for reasons I don't know (D-25 and Microdol-X
suggest 75F, at least in older literature).
This leads into an area where I have no definite
knowledge: how much difference in result is there from
variation of developing time and temperature if the target
contrast index is the same. Its evident that diluting
developer can have considerable influence on its
characteristics (grain, sharpness, effective film speed) but
dilution is one way of compensating for the excessively
short developing times gotten with higher temperatures.
D-76, whatever its faults, remains one of the most
reliable and predictable developers in existence.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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