[pure-silver] Re: Vitamin C and Hydroquinone?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 28 Jan 2005 12:18:11 -0800
----- 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
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
