[pure-silver] Re: Ilfosol S - addendum


----- Original Message ----- From: "titrisol" <titrisol@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, March 31, 2006 9:52 AM
Subject: [pure-silver] Re: Ilfosol S - addendum


I asked about the additivity of HQ and ascorbate over a year
ago.... this was the answer I got form R.Knoppow:

--- Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:


----- Original Message ----- From: "titrisol" <titrisol@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, January 28, 2005 10:22 AM
Subject: [pure-silver] Vitamin C and Hydroquinone?


> Hi all,
> I've been following the ascorbic developers attently, > for
> a
> while, and have tried "perverting" rodinal succesfully.
>
> I've seen that most developers are either Phenidone-C > or
> Metol-C
> but I haven;t seen any Hydroquinone-C developers.
> Can someone clarify why? or guide me to a resource on > this
> topic?
> - Is there anatagonism between these 2 agents?
> - Do they act similarly?
> - Is ascorbate enough with phenidone?
>
> Thanks
>
Hydroquinone and Ascorbic acid have similar functions in
developers. Together with Metol or Phenidone they act in a
way that is known as superadditive. The combined developers
are more efficient and long lived than either alone. The
chemical relationship is complex but even where the
Hydroquinone is inactive as a developing agent, as in D-76,
it still acts to regenerate the Metol. Hydroquinone and
Ascorbic acid are not antagonistic but do not mutually
support each other to become superadditive. Also, neither is
a good general purpose developing agent on its own. The only
developers using Hydroquinone as the exclusive agent are
extremely high contrast developers used for photomechanical
work.
I am not sure what you mean in the last question. If you
mean does the combination of Phenidone and Ascorbic acid
form a good, practical, developer, the answer is yes, and it
does not need the addition of a third agent.
Metol is a good developing agent on its own, as in D-23
or D-25, but D-23 has a more limited capacity than D-76
where Metol is combined with Hydroquinone. Phenidone is a
very low contrast developer on its own as in POTA. It needs
the help of another agent like Hydroquinone or Ascorbic acid
to become useful as a general purpose developer.
p-Aminophenol, the active ingredient in Rodinal, is
similar to Metol but inferior to it as a sole developer. It
is used in Rodinal because it is soluble in sufficient
quantity to make highly concentrated stock solutions. It has
not been exploited in non-concentrated developers because
other agents, particularly Metol, are superior to it. About
the only non-concentrate formulas are substitutes for Metol
where there is a concern about Metol poisoning. Those with a
sensitivity to Metol will do better with Phenidone and
Ascorbic acid developers, which are not sensitizing and are,
in general, better developers.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx


And grandmaster Ryuji added:

--- Ryuji Suzuki <rs@xxxxxxxxxxxxxxx> wrote: 

From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: Vitamin C and Hydroquinone?
Date: Fri, 28 Jan 2005 12:18:11 -0800

> Hydroquinone and Ascorbic acid are not antagonistic but > do
not
> mutually support each other to become superadditive.

Note that "superadditive" has a specific meaning that the sum
of
developing rate of A and rate of B is less than the rate of
development by A and B together, all at the same condition.
The term
"rate" here is the key. If you simply look at the "density"
built by
the developing agents, the result means different things. Thus
lack of
mutual interaction between developing agents may imply lack of
supersdditivity, but not the converse.

--
Ryuji Suzuki
"Keep a good head and always carry a light camera."


Cheers
P
Ryuji has a very much better understanding of the chemistry involved here than I do. It seems to me that he has written quite a bit on the superadditivity of various developers in his posts to this group.
One problem with MSDS is that they are often both incomplete and misleading about proportions of ingredients. Always remember that they are legal documents, not technical or scientific papers.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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