PotassiumOxalte and pH
- To: alt-photo-process-l@usask.ca
- Subject: PotassiumOxalte and pH
- From: C.Breukel@lumc.nl
- Date: Mon, 19 Feb 2007 13:00:59 +0100
- Comments: "alt-photo-process mailing list"
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- Thread-topic: 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