From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 07/17/02-09:45:16 AM Z
At 10:22 AM 07/17/2002 -0700, you wrote:
>Sandy wrote:
>
>> Pyrocat-HD is based on pyrocatechin (catechol), not pyrogallol.
>> Pyrocatechin is also toxic, but as far as I can determine no more so
>> than hydroquinone, to which it is closely related. And of course
>> hydroquinone is in D76 and most all MQ paper developers.
>
>OK, that's good to know.
>
>>
>>
>> Even so I would recommend that you avoid splashing around any
>> developer. With the exception of those based on ascorbic acid they
>> are all quite toxic, both via inhalation and via skin absorption.
>
>I didn't know that ascorbic acid was a developer! Which developers are
>based on it?
>
>I am pretty careful. I wear gloves and a mask when playing with developer.
>
>>
>> Finally, yes TRI-X is a much better film than HP5+ for getting the
>> high contrast needed for most forms of alternative printing.
>> Unfortunately it has become prohibitively expensive to purchase, even
>> with special order, for the ULF sizes in which I do much of my work.
>
>That's too bad. I love Tri X. I should have maintained my loyalty to it,
>but I was tempted by the low price of HP5+ in smaller boxes. I think I am
>going to go back to it as it's not hard to get in 8x10.
>
>--shannon
Ascorbic acid has been around for a long time as a developer. It was used
mainly in research until its environmentally friendly character and low
toxicity made it attractive.
Ilford uses it in Ilfosol-S and Kodak in Xtol, it may be in others. In
both it is used in conjunction with other developing agents. Iso-Ascorbic
acid acts in something of the same way as Hydroquinone forming
super-additive developers with Metol or Phenidone. Xtol is in some ways
similar to D-76 but using a Phenidone derivative (Kodak Dimezone) in place
of the Metol and Iso-Ascorbic acid in place of the Hydroquinone. The result
is a low toxicity developer capable of delivering higher than normal film
speed along with very fine grain.
By itself, Iso-Ascorbic acid is not very active and is not a satisfactory
developer.
There is an extensive patent literature on Ascorbic acid developers,
several hundred patents at least.
I have never used Ilfosol-S but have read reports of similar sudden loss
of activity.
---- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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