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
