[pure-silver] Re: Adding Pot Bromife to PC-TEA
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 07 Jan 2005 18:13:19 -0500 (EST)
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
Subject: [pure-silver] Re: Adding Pot Bromife to PC-TEA
Date: Fri, 7 Jan 2005 17:35:10 -0500
> I have always thought that Gainer's formulas tend to use too much
> Phenidone. His initial P/A ratio was 1:36 (0.25:9). If you make
> the necessary conversions in the Xtol formula you get a ratio of
> 1:69. Some other commercial film developers are even smaller 1:80
> or 1:90. I was wondering if this was the cause of the fog and poor
> tonal separation that I was seeing.
Optimal range of phenidone-to-ascorbate ratio varies depending on the
pH, absolute concentration and other factors like antifoggant. I think
his developers are very often off balance because he has some unusual
goals like removing sulfite, removing water, or manybe some other
photographically irrelevant goals. At one time he was trying to prove
sulfite doesn't do anything in developer, and he even sent me
negatives of his test runs. I could easily see the effect of sulfite
at 5x magnification, and even more clearly at 12x, but he didn't see
it at all. I didn't know what to say. I sent him a stack of xerox of
some background info on chemistry of developers, but I don't know what
happened after that.
The fog level is mostly determined by the phenidone level, pH, and
antifoggant. Ascorbate is out of the equation besides its influence on
pH and perhaps ionic strength when it comes to fog. Ascorbate is
pretty much incapable of developing AgX crystals by itself in presence
of gelatin.
> However, the substituted phenidones are said to be less efficient
> compared to phenidone even when the difference in molecular weight
> is taken into consideration.
Who said that in what context? Do you have a ref for that? I do know
methyl and dimethyl substitution at 4 position make some difference,
but I would like to know what is your source for this.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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