[pure-silver] Re: dichroic fog (was re-using D-76 w/Ilford Films)
- From: Eric Nelson <emanmb@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 1 Apr 2006 11:01:21 -0800 (PST)
Thanks for all the detailed info which is really
helpful.
It's interesting and valuable to know that it can be
removed, as it looks a bit unprofessional if a client
were to see this effect/defect.
Since it has no effect on printing it's not a major
worry for me BUT it is annoying to follow procedures
and still get a bugaboo. It's only visible after
drying so hopefully, if need be, I can follow your
ammonium thiosulfate procedure for removing the "fog"
once dry.
Can I use Kodak Rapid Fix with hardner (Solution "B"),
and add citric and metabisulfite to that? Do you have
a quantity of citric and metabilsulfite that you'd
recommend?
When you say bleach, I assume you mean potassium
ferricyanide which I'd be loathe to bring near a
client's originals. =) Even though I'd be treating
the base side of the film, I could see it easily
creeping 'round to the the emulsion side! Would be
just my luck.
Re: the low acidity of stop bath hypothesis; I had
wondered about that as well after reading as using a
water stop bath is touted in many instances. At the
first sign of this problem, it made some sense as my
original stop bath was more diluted than recommended,
yet the defect appeared anyway after boosting the stop
bath to recommended levels.
For the sake of simplicity, at separate mix of D-76
for Ilford films here would make the most sense for me
and/or using some other one shot developer.
My guess had been (only by deduction) that the
replenished D-76 was the culprit, but I had hoped it
might have been something else, thus allowing me to
continue use of the replenished D-76 bath for all
films.
Re:fixer, 1/2 gallon of Rapid Fix has a 30 roll
capacity here and I always overfill the Jobo tanks so
I don't have to dump and re-fill the tank halfway
through fixing.
I also do this with the developers as the Jobo can
produce "road ruts" in recommended use. I've found
that by increasing the volume from the recommended
900-1000 mls for 5 singly loaded reels in a 1500
series tank, to 1600-1700 mls combined with
intermittent lifting and using the lowest rotation
speed helps prevent that.
Thanks again Ryuji & Richard for your help!
Eric
--- Ryuji Suzuki <rs@xxxxxxxxxxxxxxx> wrote:
> Changed the subject.
>
> From: Eric Nelson <emanmb@xxxxxxxxx>
> Subject: [pure-silver] Re-using D-76 w/Ilford Films
> Date: Fri, 31 Mar 2006 22:40:18 -0800 (PST)
>
> > With Ilford 120 films I have been getting, what
> was
> > once diagnosed over the phone, dichroic fog, using
> > this replenished D-76.
> > No Kodak films are affected and I've made a new
> batch
> > with the same result.
> > I've also tried UN-replenished D-76 with no
> problems
> > straight or 1:1. The unreplenished is used only
> once.
>
> What you described sounds like dichroic fog. It
> often appears when the
> developer contains silver complex ions that can be
> reduced by the
> developing agent at or near the interface between
> the coated gelatin layer
> and the bulk solution. Its appearance is rather
> unpredictable but what
> you described makes perfect sense to me.
>
> Replenished (reused) developer contains silver
> complexed by sulfite,
> while fresh developer does not, at least until the
> developer is poured
> into the loaded tank. Some films are more
> susceptible to dichroic fog
> than others. There are MANY factors that affect
> this.
>
> > It has no effect in printing and to
> > my knowledge, cannot be removed.
>
> You can remove it in acidic ammonium thiosulfate
> fixer with very low
> pH. It's easy to make one by mixing ammonium
> thiosulfate, sodium
> metabisulfite and citric acid. It may take many
> minutes to lighten and
> disappear. Very weak bleach may also be used. Either
> case, test the
> bleach with an unimportant specimen from the same
> film/developer
> combination.
>
> > From what I was able to read about dichroic fog,
> it is
> > the result of low acidity of the stop bath but
> mine is
> > made according to directions.
>
> Unless one is doing something stupid, those are just
> harmless (and
> useless) suggestions. The rationale behind that
> suggestion is that, if
> a film developed in powerful developer (like D-19)
> is transferred to a
> nearly exhausted fixing bath without a complete
> stop, dichroic fog
> will occur. The reason for this is because developer
> is still active
> in the fixer, where lots of silver ion is available
> to form dichroic
> fog. As long as the developer is well removed from
> the emulsion, plain
> water rinse is completely capable of preventing this
> mechanism. However, based on what you described,
> your dichroic fog is
> formed in the developer stage and the chocie of stop
> bath is irrelevant.
>
> > Anyone care to hazard a guess as to what is going
> on
> > and if Ilford films "don't like" replenished D-76?
>
> I won't list but there are many factors affecting
> whether dichroic fog
> will appear or not.
>
> My guess in this particular case is the difference
> in the
> gelatin-polymer blend used for the emulsion and
> overcoat.
>
> Perhaps the easiest way to reduce the risk of
> dichroic fog like yours
> is to dilute the developer. However, diluted
> developer suffers from
> poorer keeping property and is not suitable for
> replenished system.
>
> The next easiest way is to change the developer
> formulation. You can
> reduce the amount of sulfite, but for the above
> reason, this is not
> a very good idea to go very far on this road. There
> are dozens of
> compounds that are known to prevent dichroic fog.
> Henn and Haist are
> two experts in this area. Many organic antifoggants
> tend to reduce or
> eliminate this type of fog, but the amount
> sufficient for this role is
> probably undesirable in film developers.
>
> One compound known to be effective are
> resorcinol-like 1,3-dihydroxy
> carbocyclic compounds (Kitze and Rosecrants, US
> Patent 3380828).
>
> Another well known compound is
> 2,4-dihydroxybenzophenone (Henn, USP
> 3161513). Bill Troop argues that this is the
> antistaining agent used
> in Microdol-X, but he has no hard evidence for this.
>
> Another interesting example is poly(N-vinyl)
> compounds such as
> poly(vinylpyrrolidone). (Henn, King and Surash, USP
> 3552969) This is
> the HC-110 patent. PVP is a highly water-soluble
> solid, but it makes a
> wide range of useful copolymers and I think some of
> them are
> incorporated in the binder system of modern
> emulsions. It has
> excellent adhesion and coating properties, although
> the polymer is
> water sensitive. But this last problem is something
> polymer engineers
> can solve by playing with copolymerinzation,
> blending, etc. PVP is
> also used to clarify beer and white wines (to remove
> excessive tannin,
> etc.)
>
> Silver stain similar to dichroic fog is a common
> problem in roller
> transport processors. Obviously, Ilford had a
> problem with it, and
> they got US Patent 5770351 (Long and Parker).
> Examples of this patent
> used two common antifoggants
> 1-phenyl-5-mercaptotetrazole and
> benzotriazole, which were largely effective in
> inhibiting stain (they
> call physical development in this patent) but PMT in
> particular didn't
> allow the print to be fixed completely. I have no
> experience with
> compounds in Formulae II and III of this patent.
>
> Similar problems occur in monobath developers,
> because monobath
> contains a lot of strong silver halide solvents,
> such as thiocyanate
> and thiosulfate. Haist published a number of
> compounds for this
> application, and if I remember correctly, compounds
> where thiol group
> and carboxylic group are attached to the same carbon
> are most
> effective. Examples are mercaptoisobutylic acid and
> mercaptoacetic
> acid. Both are nasty compounds.
>
>
> Of these compounds, certainly the easiest to obtain
> and safest to
> human health and environment is PVP. Resorcinol is
> easy to obtain but
> it is said to be not as effective as its alkylated
> or halogenated
> derivatives. It may be that dissolving some PVP in
> the developer may
> solve the problem...
>
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