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

Forgot to write that I also plan to clear the paper in Sodium Sulfite
after soaking it in HCl to soften the fibers in order to eliminate the
remaining CaCl2 and HCl (+ a final plain water rinse, maybe 3 - 4
changes...) Do you think this is a nice addition to the procedure? Or is
it totally unnecessary and/or harmful (due reaction products of CaCl / HCl
/ Sulfite...)?

Thanks again,

12 Ağustos 2008, Salı, 9:01 am tarihinde, Loris Medici yazmış:
> 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
> later)...
> 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,
> Loris.