[pure-silver] Re: Vitamin C and Hydroquinone?
- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
- To: "'pure-silver@xxxxxxxxxxxxx'" <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 31 Jan 2005 09:22:22 -0500
Be aware that sodium erythorbate (CAS # 6381-77-7) exists as the monohydrate.
Thus, some adjustment in weight must be made when using it in formulas that call
for sodium ascorbate anhydrous. You will have to use 9% more of the erythorbate
salt.
Jerry
-----Original Message-----
From: titrisol [mailto:titrisol@xxxxxxxxx]
Sent: Saturday, January 29, 2005 12:26 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Vitamin C and Hydroquinone?
Thnaks Richard and Ryuji,
you have answered my questions and given me more info.
I have access to erythorbic acid, which for meat processing (and I assume
photography) purposes works as well as Vit-C So I want to try search/work with
this P-C developers.
Thanks a lot!
--- 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
>
>
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