Re: Oxalic Acid Presoak for some pt/pd papers?
I'll second my thought about acidifying paper for pt/pd or other iron processes: It's better to use hydrochloric or acetic acid for that purpose. The salt you'll get from oxalic acid + calcium carbonate (the alkali buffer) is calcium oxalate -> a highly insoluble salt with a needle-like sharp crystal structure whereas both the salts you get from HCl and acetic are highly soluble (= will leave the paper in the subsequent water rinse). I use 5% hydrochloric acid for two minutes with Fabriano Artistico (Trad. and EW) with very good results - regardless the batch number. I suspect even one minute will suffice (no bubbles after about 30secs) but I keep it in the acid batch a little longer for extra safety. Probably finding HCl is easier (and cheaper) than finding oxalic acid too; just ask for muriatic acid in the hardware store. I won't talk about acetic acid -> everyday kitchen item. Anyway, the main issue is not convenience here but sanity of paper / image in the long term. I don't believe oxalic is a good idea... Regards, Loris. 28 Mart 2009, Cumartesi, 3:47 am tarihinde, Clay yazmış: > Cook and look. That's about the best advice I can give. > > I don't know if it is possible to over-acidify, but it sure is obvious > when it is under-acidified. The prints are weak and washed out. > On Mar 27, 2009, at 8:05 PM, Paul Viapiano wrote: > >> Good point, Clay...so far I've needed low dilutions, but I'll keep >> this in mind for the future. >> >> There's no way to tell ahead of time, is there? Just make a print >> and have it be sucky, I guess..? >> >> Paul >> >> >> >> ----- Original Message ----- From: "Clay" <wcharmon@wt.net> >> To: <alt-photo-process-l@usask.ca> >> Sent: Friday, March 27, 2009 5:52 PM >> Subject: Re: Oxalic Acid Presoak for some pt/pd papers? >> >> >>> Paul's suggestions are all on the mark. I would like to add a >>> footnote to item #3: >>> >>> You may need concentrations of oxalic of 5 or even in some cases >>> 8-10% to get rid of the buffering agents in Fabriano. This paper's >>> buffering can be highly variable. I am still printing from a batch >>> I bought about three years ago, and a 5 minute soak at 2% works >>> fine. Some of the more recent batches I have used in workshops >>> have needed 7.5% for 15 minutes! In short, YMMV. It is a great >>> paper, as long as the buffering has been neutralized. The trick is >>> in finding out exactly how much acid and time is needed for the >>> batch you happen to have. >>> On Mar 27, 2009, at 6:34 PM, Paul Viapiano wrote: >>> >>>> Dan, I'm sure others will chime in but my findings are: >>>> >>>> 1. Fabriano EW, Arches Cover, Rives BFK, Stonehenge >>>> >>>> 2. Helps with better dMax, and general tonality, etc...so much of >>>> today's papers are so alkaline, heavily buffered, etc that the >>>> acidic pt/pd solution hits the alkaline paper and poor results >>>> occur. >>>> >>>> 3. 1 - 1.5% oxalic acid in water for 3-5 minutes...Stan Klimek >>>> also recommends this in the Arentz addendum. I dry flat on paper >>>> towels, but hanging is ok. I just don't want my corners marked >>>> with clips. >>>> >>>> 4. The Arentz book hasa whole chapter on paper; which ones are >>>> good to go as is, which need acidification, etc... >>>> >>>> Fabriano EW is my choice with excellent results. Platine is a >>>> great paper, but I've never produced the same or as good results >>>> as the Fabriano. >>>> >>>> After acidification, the single biggest tip is to humidify the >>>> dried, coated paper pre-exposure, and after you put the neg/paper >>>> sandwich in the frame, cover it with a piece of mylar the size of >>>> the frame before you put the back on and lock it up. Keeps the >>>> humidity in the paper during exposure and wow...! That made all >>>> the difference in my printing (also from Stan Klimek)... >>>> >>>> Hope this helps... >>>> >>>> Paul >>>> >>>> >>>> >>>> ----- Original Message ----- From: "Dan Burkholder" <fdanb@aol.com> >>>> To: <alt-photo-process-l@usask.ca> >>>> Sent: Friday, March 27, 2009 4:07 PM >>>> Subject: Oxalic Acid Presoak for some pt/pd papers? >>>> >>>> >>>>> Sorry if this has been beaten to death on the list already but a >>>>> Spanish friend wants the particulars of using a weak Oxalic acid >>>>> presoak for some of his pt/pd printing. He's running into some >>>>> monster- long exposure times as he prints on hand-coated inkjet >>>>> papers. He has his reasons for doing this. Frankly, I'm >>>>> impressed he's getting the results he is using a paper that >>>>> isn't formulated for any kind of wet process. He hasn't checked >>>>> the pH of the paper and that seems like a good place to start. >>>>> In the mean time... >>>>> >>>>> Here are some questions to stir discussion: >>>>> >>>>> 1. What papers are noted to benefit from the acid presoak? >>>>> >>>>> 2. What problems (lower D-max, mottling, etc.) does the presoak >>>>> address? >>>>> >>>>> 3. What are the recommended acid dilutions and times and drying >>>>> procedures for this procedure? >>>>> >>>>> 4. And anything else that you think would help. >>>>> >>>>> I've never done the presoak thing but I am curious as to what >>>>> others have to say about it. >>>>> >>>>> Thanks in advance for any help and suggestions. >>>>> >>>>> Dan >>>>> >>>>> info@DanBurkholder.com >>>>> www.DanBurkholder.com
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