Bob and everyone-
This is an interesting idea. I don’t know of any alkaline fixers beyond TF-4
and TF-5, which are both recent formulas as far as I know. Luckily I’ve never
seen dichroic fog on my negatives yet, but the vast majority of them were fixed
in acid fixers.
I’ll consult with my wife, who is a photograph conservator, and see what she
thinks. And report back, of course.
Mark S
Sent from my iPhone
On Mar 18, 2021, at 5:21 PM, `Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
What is the theory of this? I never heard of it before. Dichroic fog is
very fine silver deposited on the film. A sort of dichroic fog can also be
generated in a hardening fixing bath when aluminum is precipitated on the
emulsion. The main purpose of a stop bath is to immediately stop development
and deliver the film to the fixing bath in an acid condition. The acid in the
fixer is there partly to keep carried over developer from becoming active
again.
Its possible there is a mechanism for production of dichroic fog where a
stop bath is not used but it may also be myth.
On 3/18/2021 3:18 PM, BOB KISS wrote:
URGENT: You really should use a stop bath with film if you are using an acid
fixer.I started doing photo conservation/archiving work nearly 30 years ago
and enlisted the aid of Jose Orraca, a world famous photo conservator, a
number of photo historians, and the remaining synapses from my under grad
and grad photo chem from RIT.Something that kept showing up in older
negatives was dichroic fog.When asked, ALL my advisors said it resulted from
the film going from alkaline developers into acid hardening fixers without
stop bath.
NOW: if you use a neutral or slightly alkaline fixer like TF-5 or most other
ammonium thiosulfate fixers, no prob.But alkaline dev to acid fixer, you
have probably cursed your negs to dichroic for in the future.Before
digitization and numerous redundant data storage systems, the negative was
revered as "the" document and the print as the artist's statement...Adams
said, the negative is the score, the print the performance.
I am sure that Richard will look into his extensive documentation and
confirm what I claim above...
*From:*pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] *On Behalf Of *MARK SAMPSON ;
(Redacted sender "msampson45" for DMARC)
*Sent:* Thursday, March 18, 2021 5:57 PM
*To:* pure-silver@xxxxxxxxxxxxx
*Subject:* [pure-silver] Re: simple stop bath recipe?
Interesting. TF-5 is alkaline and non-hardening... the lack of which has not
caused any problems with the prints. I’ve been told that TF-5 is buffered
and doesn’t require a stop bath, a water rinse is good enough. I guess I’m
being traditional by using a stop bath.
I time the stop bath for the usual 30” and have not noticed any continued
development in the fixer. Never imagined such a thing could be possible-
even after 40+ years in the craft. Live and learn!
Mark S
Sent from my iPhone
On Mar 18, 2021, at 2:17 PM, Wilbert van den Berg <wilbert@xxxxxxxxxxxxxxx>
wrote:
15 gr of citric acid in 1 liter of water.
Le 18/03/2021 à 21:58, `Richard Knoppow a écrit :
Citric acid works fine where the fixer does not have
alum hardener. It has the virtue of not having a
vinegar odor. Can also be used in non-hardening fixing
baths. Actually, fixers do not need to be acid, the
fixing action is independent of pH but they are made
acid partly because the alum hardener needs it and also
to make sure any developer carried over is inactivated.
A stop bath will usually take care of the developer but
the usual few second stop bath does not wash out the
developer which can become active again if put into an
alkaline bath.
--
wilbert@xxxxxxxxxxxxxxx <mailto:wilbert@xxxxxxxxxxxxxxx>
04 73 72 19 20
"Quand on se retrouve du côté de la majorité, il est temps de prendre du
recul et de réfléchir."
Mark Twain
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
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