U of S | Mailing List Archive | alt-photo-process-l | Re: ferro vs ferri

Re: ferro vs ferri

From: Trevor Cunningham <tr_cunningham@yahoo.com>
Subject: Re: ferro vs ferri
Date: Thu, 30 Aug 2007 22:05:36 -0700 (PDT)

> The local company stocks what they call potassium
> hexacyanoferrate, but when I ask them about the (III)
> portion of the nomenclature I begin to loose clarity.

That's plain unacceptable. But if the chemical dealer sells
the same stuff as ferrocyanide, then that just gives you the
info ... it's (II). You could also ask for the CAS number.

Another way is to demand a sample and test it yourself. You
can make a solution of the stuff, hook up two steel nails with
a 9V battery, and immerse the nails into the solution. If you
see the anode forming prussian blue pigment around it, it's
(II).  Or you can mix it with ferric chloride or something and
see if it makes the pigment. If you immerse processed b&w
print into the solution and if the image becomes lighter, it's

> Did you happen to write how to make K-Ferricyanide from
> scratch?

I didn't and I wouldn't. The thing is that you must have a
serious safety facility and willing to go through the steps to
make it. However, if what you need is K-HCF (III) you can make
it from a solution of K-HCF (II) by completely oxidizing it
with moderately strong oxidizing agents, such as ozone or
peroxide, and then removing excess ozone or peroxide by
evaporating the solution in vacuum or something. This is a bit
safER than making it from scratch, but the process is involved
and again, it's probably more than what you are willing to do.

Simply, in this case, no amount of help I can give you here
can substitute for a competent chemical dealer.

Ryuji Suzuki