Re: Modifying bleaches

From: Charlie Goodwin <cgoodwin@mcttelecom.com>
Subject: Re: Modifying bleaches
Date: Wed, 01 Dec 2004 12:40:52 -0500

> That is one of the items I was most wondering about. Reading about
  ferricyanide brings you to such warnings, yet the DuPont formula has
  no such warning as listed in "The Darkroom Cookbook". I am very
  glad you have reiterated the issue for me.

Ferricyanide itself is not that dangerous in ordinary darkroom use. I
would not shine UV light or strong visible light to it though. You can
make ordinary bleach with any of the halide and optionally a pH
buffer. But I would not recommend to use a strong acid if you aren't
very familiar with chemistry of this compound.

There is a way to vary the oxidation power of the bleach but I don't
have time to get into details today. Basically you can mix ferri and
ferrocyanide at varying proportions to make redox buffer. You can get
similar effect by replenishing old bleach with fresh one. Fresh bleach
is pretty vigorous and strong, but used ones are more gentle and
stable. Anyway, start saving test strips so that you have a lot of
scrap prints to test the bleach/toning on.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)