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Developers Don't Last Forever

Everyone knows that for Platinum printing, potassium oxalate developer lasts "forever", you can just keep using it. This advice is found all over the web.

This may work for some people, possibly depending on how much printing you're doing and what papers you're working with. I've found it doesn't work for me.

I was printing and developing with potassium oxalate developer (I still use KOx, it's my standard developer), just reusing the developer as usual. After a long weekend of printing, I started having problems. Print contrast was wonky and images were suddenly really grainy. I assumed the problem was that my ferric oxalate was bad, so I switched to a fresh batch, but that didn't help. After spending some time on Google, DPUG, and AltPhoto, I learned that some printers were acidifying their potassium oxalate and also replenishing it.

The bottom line: after switching to routine replenishing and acidifying the developer the problems stopped (and never came back).

Technical note: I acidify potassium oxalate developer by adding enough oxalic acid to bring the pH just below neutral, adding a few grams per liter. I replenish the developer by replacing 1 ml of used developer with 1 ml of fresh developer for each square inch of paper that goes through the developer. So for each 11x14, I'll replace about 150 ml of developer. It's a lot less expensive than wasting Platinum.