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

Eliminating CaCO3 in buffer in "achival" watercolor papers

  • To: alt-photo-process-l@usask.ca
  • Subject: Eliminating CaCO3 in buffer in "achival" watercolor papers
  • From: Loris Medici <mail@loris.medici.name>
  • Date: Tue, 12 Aug 2008 09:01:40 +0300 (EEST)
  • Comments: "alt-photo-process mailing list"
  • Delivered-to: alt-photo-process-l-archive@www.usask.ca
  • Importance: Normal
  • List-id: alt-photo-process mailing list <alt-photo-process-l@sask.usask.ca>
  • Reply-to: alt-photo-process-l@usask.ca
  • User-agent: SquirrelMail/1.4.9a

Hi all, this question goes to chemists and/or papermakers especially:

Albeit I like COT 320 for iron based alternative processes (such as
Cyanotype, Vandyke / Kallitype, Pt/Pd...), I have to import this paper and
cost is high. I can find nice Fabriano Artistico (Trad. White) paper at
good prices locally; the distributor is running an aggressive pricing
policy due to competition + they're very helpful / willing to bring
(not-much-sought-by-watercolor-artists) smooth HP papers just for me.

Anyway, this paper incorporates a CaCO3 alkali buffer (hence the
designation "archival") which is fatal to iron processes. I tried to
neutralize the paper with Oxalic Acid before and it was a disaster. IMO,
Oxalic Acid is not a good way to go since CaCO3 + Oxalic Acid forms
unsoluble compound Calcium Oxalate (kidney stones!) which crystals are
very sharp and a) makes the surface gritty (very strong effect with
Artistico), b) sharp crystals will eventually cut the paper's fibers and
weaken it (due to movement in development / rinse stages and when handling

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.)

What do you think? Is that a good / sound way to go? Any other suggestions?

Thanks in advance,