Re: Eliminating CaCO3 in buffer in "achival" watercolor papers
Citrate forms a soluble calcium complex in alkaline environment. These things depend heavily on the form of anion, and the reacting agent also competes with water, so the result is very pH dependent. However, citrate is not as effective as tartrate, gluconate or saccharate in removing calcium. EDTA, NTA, DTPA, polyphosphates are also very effective in removing calcium, again, in alkaline side of the pH scale. -- 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: Re: Eliminating CaCO3 in buffer in "achival" watercolor papers Date: Tue, 12 Aug 2008 13:29:29 +0300 (EEST) > Thanks Diana, > > I also thought about citric acid but the product is insoluble Calcium > Citrate (a food additive), thus, it remains in the paper. I'd prefer > something that totally leaves the paper. Calcium citrate may interfere > with the process I intend to use - maybe that's why you didn't get perfect > results... > > Thanks again, > Loris. > > > 12 Ağustos 2008, Salı, 9:16 am tarihinde, dhbloomfield@bellsouth.net yazmış: > > > > > > Hi Loris, > > > > 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. > > > > Diana -------------- Original message from Loris Medici > > <mail@loris.medici.name>: -------------- > > > > > >> 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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