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

Loris wrote:

I was searching for a highly soluble Ca compound and found it to be CaCl2
(Calcium Chloride). To get CaCl2 from CaCO3, you have to react it with HCl
(Hydrochloric Acid)(other byproducts are CO2 and water) HCl too is harmful
to paper fibers (may lead to yellowing and brittle the paper later...) but
I know that it was used (and maybe still used) by Pt/Pd printers as a
clearing agent.

So, I need ballpark figures (to start testing) for strenght (of HCl
solution) and lenght of reaction (soak time) in order to get rid of CaCO3
in Artistico paper which is not harmful to the paper. Can you make
suggestions? I plan to use 1% HCl and soak the paper in it for 5 minutes.
Is that too long/short and/or do you think I should use a milder/stronger
HCl strenght? I know this depends much on paper (how much CaCO3 it
contains ect.)
I still use HCl to clear Pt prints, and an HCl pre-coating bath (in both cases, followed by a tap water wash and two distilled water rinses). The pre-coating bath (i) neutralizes any alkaline buffering agent and (ii) dissolves the microscopic metal flecks that sometimes appear in paper (from worn calendaring rollers, I'm told) and ruin Pt prints. I generally use 0.5% HCl for both, although I have used up to 2% in the pre-coating bath for some troublesome papers. My routine is 10 minutes prior to coating, 5 minutes to clear.

Best regards,