[pure-silver] Re: Adding Pot Bromife to PC-TEA
- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
- To: "'pure-silver@xxxxxxxxxxxxx'" <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 10 Jan 2005 12:08:02 -0500
What the article said was that even after adjusting for the difference in
molecular weight, replacing Phenidone with a substituted Phenidone resulted in
somewhat less activity. I read this on the internet but couldn't find a
reference in my notes. I may not have kept a copy since the article did not
give specific values.
Jerry
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx [mailto:pure-silver-bounce@xxxxxxxxxxxxx]
On Behalf Of Ryuji Suzuki
Sent: Friday, January 07, 2005 6:13 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Adding Pot Bromife to PC-TEA
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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