Re: Eliminating CaCO3 in buffer in "achival" watercolor papers
In order to wash out calcium, I suggest an alkaline solution of potassium sodium tartrate, an alkaline solution of potassium sodium saccharate, an alkaline solution of sodium gluconate or Na4EDTA solution. These would be my first choice. Besides, though less effectively, you could use an alkaline solution of sodium citrate. As a starting point, I'd suggest 1% of any of the above agent and 1% sodium hydroxide, and soak the paper in the solution with intermittent agitation until you find the paper has lost the calcium salt, as determined by test prints or whatever means you prefer. Na4EDTA does not need additional NaOH and it may be effective at an even lower concentration. However, EDTA is not biodegradable (and in some areas of Germany and perhaps other areas, EDTA pollution is a problem). Once you treat the paper, you may wish to rinse off the chelating agent and also neutralize the paper to the acidic side. I suggest to use a dilute solution of acetic acid for this. -- Ryuji Suzuki "Strange how people who suffer together have stronger connections than people who are most content." (Bob Dylan, Brownsville Girl, 1986) From: Loris Medici <mail@loris.medici.name> Subject: Eliminating CaCO3 in buffer in "achival" watercolor papers Date: Tue, 12 Aug 2008 09:01:40 +0300 (EEST) > 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. > >
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