Re: Iron

I don't have a reference at hand in my office right now, but I think
EDTA is most efficient in complex iron at pH of around 6. Depending on
which salt you are using, the pH may be lower. Addition of sulfite or
KHCA may bring the pH to 6-8 range.

In response to others posting lack of fading symptom of VDB prints, I
think there is some misunderstanding of the point. The context of
iron-EDTA thing was deterioration of paper substrate and not the image.
In the iron-gall inked paper I was referring to, the inked area is
destroyed or very easily destroyed with little mechanical force.

For the image part, I know hydrogen peroxide at 500-3000ppm range is
enough to bleach out silver image in a matter of days, unless the silver
image is toned. While 500ppm is an artificially high level to accelerate
the testing, peroxide is given off from cardboard, paint, adhesive, etc.
and I personally want to make my images quite resistant to peroxide
attacks. There are environmental oxidants other than peroxide as well.

In discussing longevity of images, storage condition is a big factor.
Temp, humidity, etc. If humidity is higher, environmental oxidants are
more easily going into the paper, and the silver is also more reactive
with them. (When you read darkroom cookbook and stuff like that, you'll
see them talking about silver solvent = sodium sulfite, but don't forget
water is a silver solvent as well!) Considering how much PITA to keep
photographic prints in strictly controlled conditions, I think it's a
lot easier to process the material in such a way to minimize the
environmental influence on the image, and ease the stroage/display
condition to more manageable level.

On Mon, 27 Mar 2006 09:27:20 -0800, "Kerik" <kerik@kerik.com> said:
>
> > I have a good sample of ten year old prints cleared in EDTA/sodium
> > sulfite that look as good as the day they were made. I have not
> > personally seen any EDTA cleared prints that have degraded, but by no
> > means have I seen every
> > print ever made and cleared with this method.
>
> I think the issue may be that EDTA by itself doesn't work very well for
> clearing pt/pd. I've had many comments from workshop students who had
> previously tried EDTA alone and reported such problems, but adding sodium
> sulfite to the mix did the trick. Approx one tablespoon each of EDTA and
> sodium sulfite per liter works well on most papers, as does Kodak Hypo
> Clearing Agent and Heico Permawash.
>
> Kerik
Received on Mon Mar 27 14:06:35 2006