RE: PotassiumOxalte and pH
Hello Cor, I also noticed that in the past. It depends on the batch you get. Some suppliers are not that precise as you would expect. Arcos seems to be consistent in their PotOx. Regards, Witho -----Oorspronkelijk bericht----- Van: C.Breukel@lumc.nl [mailto:C.Breukel@lumc.nl] Verzonden: maandag 19 februari 2007 13:01 Aan: alt-photo-process-l@usask.ca Onderwerp: 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
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