Re: Eliminating CaCO3 in buffer in "achival" watercolor papers
Not a chemist here, but I also had a horrible time trying to soak Fabriano in oxalic acid, specifically in preparation for pt/pd printing. Seems like I had to be extremely precise with everything; otherwise it was a disaster. I could never get it consistently even (the soaking, the amount I used, or something). Anyway, something came up about this once in a conversation with Mike Ware. He said that he thought oxalic acid was the wrong way to go, and he believed citric acid would be a much better choice-- and gave all the reasons why. That was some time ago, but if I can find that email, I'll forward it on. So I did try the citric acid, and it worked much better, though I never got an idea of the right amount to use, how long to soak, etc-- so it was never perfect (though 100 times better than the oxalic acid soak). I got busy and on to something else and never continued with it. or followed up about exact amounts, etc., but it did work.
-------------- Original message from Loris Medici <email@example.com>: --------------
> 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,