U of S | Mailing List Archive | alt-photo-process-l | RE: PotassiumOxalate and pH

RE: PotassiumOxalate and pH



Cor, I recall the pH of fresh Pot Ox as I recorded it to be closer to 5.4. I
can't find my paper that has that note on it right now. I need to do a
little filing : ( 

In doing a quick google, several listed it at 7 +/- 1 but I did see
references to 5.5 and some msds show no information under pH. 


Eric Neilsen Photography
4101 Commerce Street
Suite 9
Dallas, TX 75226
http://e.neilsen.home.att.net
http://ericneilsenphotography.com
Skype ejprinter

> -----Original Message-----
> From: C.Breukel@lumc.nl [mailto:C.Breukel@lumc.nl]
> Sent: Monday, February 19, 2007 6:01 AM
> To: alt-photo-process-l@usask.ca
> Subject: PotassiumOxalte and pH
> 
> In the past I was well advised about how to keep the PotOx solution for
> pure Pt printing alive:
> 
> Regularly filter off the debris
> Replenish with fresh 25% PotOX (keep the end volume constant)
> Keep the pH on the acid side (around pH 4) with oxalic acid
> 
> Today I was checking the pH again (got some problems with pt printing),
> and the solution was around pH7, so I added the oxalic acid.
> 
> At the same time I made some fresh 25% PotOx, checked the pH, and saw
> that it was pH 8.0! I was surprised, because I assumed it to be on the
> acid side. (Checked the literature, and indeed potOx is neutral to
> slightly basic, and off course no buffer).
> 
> This seems to be contradicting: when your used PotOx solution gives
> problems: use oxalic acid to lower the pH (and that sure works), but
> OTOH: the pH of the fresh starting solution is neutral/slightly basic?
> 
> What am I missing? I guess when the developer gets used, a lot of other
> stuff gets introduced: ferric compounds, Pt compounds, perhaps paper
> compounds, and then a lower pH is necessary.
> 
> Best,
> 
> Cor