Re: Another Ziatype question

Actually, it does remove iron from the surface of stainless steel. There is
a test, where electrons are bounced off of a metal surface. Citric and
phosphoric acids actually produce an iron depleted surface. It's only a few
molecules thick, but it is a measurable change.

For really tough stains, the company we contract with uses hydrofluoric acid
(HF). That would clear a print so that even the paper is gone!!

Martin Angerman

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>; <paleophoto@adelphia.net>
Sent: Tuesday, October 12, 2004 4:17 AM
Subject: Re: Another Ziatype question

> From: Martin Angerman <paleophoto@adelphia.net>
> Subject: Re: Another Ziatype question
> Date: Mon, 11 Oct 2004 20:28:04 -0700
>
> > We have a lot of stainless steel piping at work. Part of the major
> > maintenance is called "passivation." Essentially it removes any surface
> > iron oxide, giving a chrome and nickel rich surface. The preferred
> > chemicals are citric acid with EDTA, followed by citric acid alone, then
> > phosphoric.
>
> I bet this treatment is doen to increase the corrosion resistance
> rather than to remove iron as discussed here. Of course EDTA and
> citric acid mixture helps to reduce iron but phosphoric acid would
> convert iron to iron phosphate, which is very insoluble.
>
> > As far as to which type of EDTA to use, as a general chemistry
> > reagent, the main difference is in the solubility. Once again,
> > usually in much greater concentrations than for printing.
>
> They also differ in acidity. I think solubility is not much of an
> issue here, because EDTA is often used way below solubility limit.
>
> --
> Ryuji Suzuki
> "You have to realize that junk is not the problem in and of itself.
> Junk is the symptom, not the problem."
> (Bob Dylan 1971; source: No Direction Home by Robert Shelton)
Received on Tue Oct 12 19:49:01 2004