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 > > ============================================================================================================= > 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. > __________________________________ Do you Yahoo!? Yahoo! Mail - Easier than ever with enhanced search. Learn more. http://info.mail.yahoo.com/mail_250 ============================================================================================================= 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.