RE: acid pre-soak

Etienne, Have you or anyone you know try a bath of disodium edta after an
acid bath and wash? I will test a few papers that I have around the studio
this week and let you all know what happens.

Eric Neilsen Photography
4101 Commerce Street
Suite 9
Dallas, TX 75226
http://e.neilsen.home.att.net
http://ericneilsenphotography.com
 
> -----Original Message-----
> From: Etienne Garbaux [mailto:photographeur@softhome.net]
> Sent: Monday, August 15, 2005 6:34 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: RE: acid pre-soak
>
> Sandy wrote:
>
> > Why rinse in water after the acid pre-soak? Most people I know who
> > use the oxalic acid pre-soak just pull the print from the acid bath
> > and hang it to dry.
>
> First, note that I have tried a number of acids, but not oxalic acid. In
> processes that already employ oxalates, some extra oxalate ion may be
> benign in a way that extra citrate, phosphate, chlorine, or sulfur ions
> may
> not be. Presumably, it is approximately equivalent to adding a bit of
> oxalic acid to the coating solution.
>
> My use of the acid bath is exclusively to neutralize the alkali (generally
> calcium carbonate), not to adjust the chemistry of the process itself.
> Once that is done, I see no reason to leave the byproducts and excess acid
> in the paper.
>
> Speaking of byproducts: calcium oxalate is soluble only in miniscule
> amounts (which, incidentally, is why the majority of kidney stones are
> composed of it). Thus, when you neutralize calcium carbonate with oxalic
> acid, you precipitate basically all of the calcium as calcium oxalate. I
> don't know that this is problematic, but doubt that it provides any
> benefit. Just one more contaminant (where contaminant is defined as
> something other than paper fiber (cellulose) or platinum metal (in the
> case
> of Pt prints)). Note that because of its low solubility, the calcium
> oxalate probably wouldn't be removed by a water wash, which is why I've
> never tried oxalic acid. Calcium citrate, calcium nitrate, and calcium
> chloride are more soluble -- thus, using citric, nitric, or hydrochloric
> acid avoids this problem.
>
> Best regards,
>
> etienne
Received on Mon Aug 15 17:57:12 2005