[rollei_list] Re: was Rollei Retro Film now is Rodinal pin holes

Richard, or anyone,  do you know what exactly is the cause of pin holes 
in film?  I have tried to research it and find a lot of recommendations 
to avoid stop bath and then I read opinions that stop bath don't really 
do it.  I have just processed some ACROS in Rodinal 1:50 and it is 
beautiful but has lots of tiny pin holes.  I use this film a lot and 
have never encountered pin holes before, processing in XTOL or Beutlers 
or R09.  Are pin holes somehow created in development?
thanks if you know and even if you don't
Dennis




>
>      There seems to be a cult about alkaline processing.
> This is at least partially based on a mis-understanding of
> how hardeners affect washing.
>      First of all, hypo does not need to be acid, the acid
> is required by the commonly used white alum hardener
> (properly potassium aluminum sulfate). Alum works when the
> pH of the bath its in is within a certain pH window.
> However, hypo, either sodium or ammonium (rapid) type will
> work at almost any pH.
>      Now, why should fixer be acid if its needed only for
> the hardener?  There are a couple of reasons. One is that
> developer can't operate in a strongly acid bath. So, in
> order to insure development is stopped at a definite point
> one must use an acid stop bath followed by an acid fixing
> bath. A water wash does not stop the development right away
> and simply rinsing the film in water leaves quite a lot of
> developer in the emulsion. For paper on untreated paper
> support (so called fiber base paper) the paper base will
> soak up a lot of developer and carry it over to the stop
> bath and fixing bath. A definite wash step is needed if an
> acid stop bath is not used to deactivate the developer.
> Actually, there is some chance of staining in a water stop
> (not very great) because the developer continues to work
> without only the carried over sulfite to prevent reaction
> products from forming. In any case an acid stop bath
> followed by an acid fixing bath, with or without hardener,
> prevents a lot more problems than it causes.
>      Now, about washing. It was found long ago in research
> carried out at Kodak and at Agfa that emulsion treated in an
> acid hardening fixing bath washed out much more slowly than
> emulsion treated in a neutral or akaline bath. The retarding
> of washing rate was especially noticable when a white alum
> hardener was used. Kodak experimented with comparing fixing
> baths with white alum to fixing baths with chrome alum
> (potassium chromium sulfate). Chrome alum (a misnomer since
> there is no aluminum in it) must operate at a much lower pH
> (much more acid) than white alum. Even so it does not show
> the strong restraining effect on washing of white alum. So,
> Kodak concluded that there was something specific about
> white alum which was causing the effect. In fact, there are
> two things happening: one is that white alum, when in an
> acid condition, acts to bind thiosulfate and
> thiosulfate-silver complexes, the later the result of the
> fixing process, to the image silver and to the gelatin. The
> bond is quite strong so washing out of these materials is
> made much longer. The second effect is from the acid itself.
> Gelatin is what is called amphoteric, that is, it has no
> definite pH of its own. It takes on the characteristics of
> whatever bath it was in last. That is, if treated in an acid
> bath it acts like an acid and if treated in an alkaline bath
> it behaves like an alkali. However, gelatin _does_ have a
> preferred pH. This is called the isoelectric point and has
> to do with the way the gelatin was manufactured. For most
> photographic gelatin the isoelectric point is just on the
> acid side of neutral. The term isoelectric comes from the
> fact that the net electric charge on the molecules of the
> gelatin is neutral when its at this point. This is important
> to washing because the thiosulfate ions and those of the
> fixer reaction products carry a charge such that that are
> attracted to the gelatin when the gelatin is more acid than
> the isoelectric point and repelled from it when the gelatin
> is more alkaline.
>     It also turns out that white alum looses its hardening
> effect if the gelatin is made too alkaline but will retain
> most of it when its about neutral.
>     It was discovered in the early 1930's at both Kodak and
> Agfa that treating film or paper in an alkaline bath after
> fixing but before washing would much accelerate washing.
> However it would also destroy the hardening effect. Various
> substances were suggested, sodium carbonate (agfa) ammonium
> carbonate, Kodalk, even Borax (Kodak) all at around a 2%
> concentration. All work but none preserves the hardening
> action.
>     Sometime before 1900 it was discovered that sea water
> was more effective in washing than fresh water but the
> reason was not known. It was known that a fresh water rinse
> had to follow the sea water wash if the images were to be
> permanent. When sea water washing became imperative during
> WW-2, especially for ship board operation extensive research
> was done for find the reason for the effect.
>     Kodak discovered that it was partly due to pH but mostly
> due to the ion exchange properties of some of the salts in
> sea water. After considerable research Kodak discovered that
> the most effective salt was a sulifite, the cation not being
> particularly important. From this Kodak developed Kodak Hypo
> Clearing Agent. This consists of about 2% sodium sulfite
> buffered to neutral with sodium bisulfite and containing two
> sequestering agents. Kodak found that at neutral pH, as
> provided by this bath, the binding effect of the acid due to
> electrical charge was broken (the pH being below the
> isoelectric point), the pH was outside of the window where
> white alum has binding action on fixer and its reaction
> products but is NOT outside the pH window where the
> hardening cross-linking is undone. In addition sulfite has a
> specific ion exchange affinity for thiosulfate and its
> silver complexes. So, by its use washing is accelerated even
> beyond the rate yielded by a simple akaline bath and the
> rate does not depend on the pH of the fixing bath or on
> whether it has alum hardener or not.
>     The sequestering agents, sodium citrate and EDTA
> tetra-sodium salt, are present for two reasons: one is to
> prevent a deposition of aluminum salts from the hardener on
> the surface of the film or paper, the other is to hold in
> suspension any mineral impurities in the water (mostly the
> magnesium  and calciumcarbonate consitituting the "hardness"
> in water which would also form hard-to-remove deposits).
>     Since this wash aid is capable of un-binding some
> incompletely converted fixer reaction products it also has
> the effect of increasing fixer capacity a bit.
>     In any case, when such a wash aid is used there is
> absolutely no advantage of a non-hardening or a non-acid
> fixing bath.
>     Even though some modern B&W films have very hard
> emulsions not all do and there is still some advantage to
> the hardener in preventing damage to the film when its wet
> (the hardener has little or no effect on dry film).
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
> Rollei List
>
> - Post to rollei_list@xxxxxxxxxxxxx
>
> - Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe'
> in the subject field OR by logging into www.freelists.org
>
> - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
> 'unsubscribe' in the subject field OR by logging into www.freelists.org
>
> - Online, searchable archives are available at
> http://www.freelists.org/archives/rollei_list
>

---
Rollei List

- Post to rollei_list@xxxxxxxxxxxxx

- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe' 
in the subject field OR by logging into www.freelists.org

- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with 
'unsubscribe' in the subject field OR by logging into www.freelists.org

- Online, searchable archives are available at
http://www.freelists.org/archives/rollei_list

Other related posts: