U of S | Mailing List Archive | alt-photo-process-l | Re: Eliminating CaCO3 in buffer in "achival" watercolor papers

Re: Eliminating CaCO3 in buffer in "achival" watercolor papers

Acetic acid is rather a poor choice to dissolve calcium
carbonate, despite the high solubility of calcium acetate.
This is because carbonate is still present in the solution and
the dissolution is partly a competition between acetate adn
carbonate. The question is which one binds calcium to make a
more stable form at the given condition. In other words,
acetic acid may break down calcium carbonate momentarily, but
then the free calcium ion is abundantly available to react
with something else, such as carbonate. This is because
calcium acetate is not very stable in water. On the other
hand, if you used EDTA, Ca-EDTA complex is so stable that you
won't see many free calcium ions in the bath and the removed
calcium is unavailable to react with carbonate or other things
that may be present in the bath.

In order to dissolve calcium carbonate effectively, you will
need a chelating agent with a high stability constant with

Ryuji Suzuki
"Strange how people who suffer together have stronger connections
than people who are most content." (Bob Dylan, Brownsville Girl, 1986)

From: Loris Medici <mail@loris.medici.name>
Subject: Re: Eliminating CaCO3 in buffer in "achival" watercolor papers
Date: Wed, 13 Aug 2008 14:17:21 +0300 (EEST)

> Thanks Dirk,
> This is reassuring -> will try the acetic acid way. BTW, I'll prefer to
> use pure acetic acid since vinegar contains other unwanted compounds.
> Regards,
> Loris.
> 12 Ağustos 2008, Salı, 2:09 pm tarihinde, Dirk-Jan Treffers yazmış:
> > Hi Loris,
> >
> > Indeed, acetic acid might be a good solution to your problem. Regular
> > houshold vinegar (usually a 4% acetic acid solution) will probably do
> > just fine.
> > Calcium acetate indeed has good solubility characteristics in water.
> > There are more products that will result in water soluble salts to
> > clear any CaCO3, but they probably will ruin your paper, or are very
> > damaging to your health (HCl, HBr, Benzoic acid, chromic acid, to name
> > a few...).
> >
> > According to my chemical books from university (I studied chemistry),
> > acidic acid is by far the most preferable option. And household
> > vinegar is the easiest form it comes in :-)
> >
> > kind regards,
> >
> > Dirk-Jan