John <use_net RemoveThis @puresilver.org> wrote in message news:<0hfcp0dk2pvdarf2d37b1a4cda2kd7illu RemoveThis @4ax.com>...
> On Sat, 13 Nov 2004 03:27:18 -0800, "Richard Knoppow"
> <dickburk RemoveThis @ix.netcom.com> wrote:
>
> Richard,
>
> Great post as usual.
>
> <snip>
>
> > Because modern stop baths were devised to work with or
> >without a stop bath they are heavily buffered by using a
> >combination of Acetic acid and Boric acid.
>
> Perhaps you meant "fixing baths" ?
>
> >Monobaths are not simply a mixture of developer
> >and fixer. They must be very carefully formulated and
> >matched to a specific emulsion. They have some very
> >interesting properties, not least of which is very
> >considerable immunity to temperature and time variations.
> >Haist shows some examples suggesting the possible image
> >quality is very high. For some reason monobaths have never
> >become popular except for some special rapid access uses.
>
> I think it's just as you indicated that they need to be
> formulated for specific films and I would add that those formulas were
> used one-shot and probably had limited stability due to the high
> alkalinity. The formulas that I'm familiar with use hydroxide as an
> accelerator. Perhaps there are other agents used ?
>
> Regards,
>
<font color=purple> > John S. Douglas, Photographer - <a style='text-decoration: underline;' href="http://www.puresilver.org</font" target="_blank">http://www.puresilver.org</font</a>>
> Please remove the "_" when replying via email
Of course, I meant fixing bath although buffered stop baths are
also possible and will have a longer life than a plain acetic or
citric acid bath.
Grant Haist goes quite deeply into monobaths, evidently this was a
subject of his research work at Kodak. Many monobaths do use sodium
hydroxide as the accelerator, the reason is simple: the developer must
compete with the fixer. Development must be completed before enough of
he halide is removed to destroy the image. Monobaths must also contain
a hardener. Haist has formulas with Glutaraldehyde but also lists a
number of oganic hardeners suitable for use in highly alkaline baths.
In both of his books Haist shows formulas optimized for Tri-X (roll
film) and Verichrome Pan, I think a couple of others but I am away
from my books at the moment. At least a couple of these formulas
include Phenidone as a primary developing agent.
I should point out that the hardener in fixing baths was intended
to compensate for the swelling caused by both the alkaline developer
and the acid fixer. Auxilliary hardeners are less necessary where the
pH of the solutions does not vary from neutral by much. Eliminating
the stop bath is attractive but there is still the problem of stopping
the development quickly and keeping developer from carrying over to a
neutral or alkaline fixing bath where it can continue development. A
long rinse in running water seems to be the solution. This is the
method used in alkaline color processing. Rinses are typically 1 to 3
minutes.
Where highly alkaline developers are used, such as lithographic
developers, it is common practice to use an anti-swelling stop bath.
Typically this has about 15 grams/liter of Sodium sulfate in it
(sulfate not sulfite). Sulfate is also used in tropical developers to
reduce emulsion swelling and slow the rate of development. Since many
B&W films, for instance T-Max, are now made to withstand 100F
processing such measures are not necessary for them. However, films
like Tri-X are still relatively sensitive to emulsion swelling. It was
also common in tropical processing and lith processing to use a
chrome-alum stop bath. Chrome alum is acid and is a very effective
hardener. However, it must operate at very low pH (around 2.0) so is
difficult to incorporate into fixing baths although there are chrome
alum fixing baths. Its use is probably not necessary for any film
these days.
With all the talk about alkaline processing and eliminating stop
baths it seems to have gotten lost that this procedure has been used
with completely satisfactory results for many decades. The proper use
of an acid stop bath stops development quickly and prevents carryover
of active developer into the fixing bath. It also prevents the
possible generation of developer stain where it is allowed to continue
in a bath without sulfite.
It also seems to me than in reading the reasons for not using acid
stop baths I am really seeing complaints of problems from bad
practice. Even complaints about odor can be solved by using acids
other than Acetic acid.
Pin holes are extremely unlikely to be caused by any conventional
packaged developer or fixer. For one thing modern emulsions are not
very vulnerable to it and very few current film developers use
carbonate, the villan in outgassing. A pinhole is an actual disruption
of the emulsion. I suspect that very often what people are seeing are
small clear spots caused by dust on the negative. Pin holes CAN occur
because of coating problems. These exist in the emulsion from the
manufacturer. A very great deal of research and technical development
has gone into making very consistent coatings. This is very well
established technology but even the best manufacturers may have
problems especially in these days of low sales and cost cutting.
Personally, I suspect the whole movement to use alkaline processing
is a sort of belief in black magic. Well, folks, there just isn't any
black magic in photographic chemistry anymore. Even emulsion making,
once one of the most closely guarded proprietary secrets in any
industry, are now public record and anyone who is willing to do some
research, AND has a decent understanding of organic and colloid
chemistry, can find out how its done.
Now, watch the flames come:-)
Richard Knoppow
Los Angeles, CA, USA
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