[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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