What's the best way to store pt/pd chemicals?

[Ian Leake]

The title says it all really: what's the best way to store pt/pd chemicals? Is the temperature significant? Light? Do some conditions enhance the crystallisation of the metals and others slow it down? I haven't seen much discussion of this and I'm wondering what's best.

 

[Jim Noel]

I store my ferric oxalate in a refrigerator. The metal salt solutions are stored n the darkroom on a shelf.
About an hour prior to printing, I take the oxalate out to warm up to room temperature. Everything is in small brown dropper bottles. I have had oxalate remain active and useful for well over a year, and never had a problem with the metal salt solutions.

 

[Ian Leake]

I keep everything in small brown bottles in my darkroom. I buy Ferric Oxalate in powder form and once in solution I get through it so fast that shelf life isn't a concern. I guess what I'm wondering is whether there's a way to minimise the appearance of crystals/precipitate in the metal solutions. These are a nightmare if they sneak into the paper coating, and filtering is so wasteful as so much good solution is absorbed into the filter paper. I don't know how or why the crystals are formed so it's hard for me to guess if there's a way to minimise them.

 

[Brian Bullen]

These are a nightmare if they sneak into the paper coating, and filtering is so wasteful as so much good solution is absorbed into the filter paper.

Ian is it possible to pre-wet the filters with distilled water so that the solution doesn't soak in as much? Just a little damp, not dripping wet. Maybe someone has tried this?

 

[TheFlyingCamera]

Ian-

I just had a chat with the folks at Bostick & Sullivan about this very topic - well, the crystals forming in platinum anyway. Depending on the crystal type, they're easy to deal with. For platinum, if you see the large, chemistry-set type crystals forming in your solution, just heat and shake, and they will dissolve. If you are getting the black scunge sedimenting out on the bottom of the bottle, while it seems like a pain and a waste, A: there's not much you can do about it, and B: it actually represents very little metal salt and is not worth hassling over until you accumulate a substantial volume of it. Best bet to deal with it is to not stir it up into your working solution before eye-droppering your working volume out of the bottle. You'll probably lose more active metal salts to the filter paper than you will to the black scunge itself, if you try to filter it.

 

[Ian Leake]

Thanks Scott - do you know if it's the crystals or the scunge that causes the black dots to appear on the print? I have both crystals and scunge and filtering does have a dramatic effect on the number of black dots on the print, but I'm still getting more of them than I like...

 

[TheFlyingCamera]

It's most likely the scunge. If you have the big crystals, just heat your pt solution with a coffee-mug warmer or in a dish of hot water until they re-dissolve. Filtering out the big crystalline structures will remove significant quantities of useable platinum from your solution, and there's no need to remove them when they'll re-dissolve. The black scunge is pure platinum that has dissociated from the chloride. That's the un-useable stuff.

 

[Ian Leake]

Thanks Scott - maybe I should scrape all the scunge up and sell it on ebay - someone must want some pure platinum

 

[TheFlyingCamera]

Actually, you can send it back to Bostick & Sullivan and they'll reclaim it for you and either send you replacement Pt or money. Contact them for more information. Be aware that all that black scunge usually adds up to thousandths of a gram. If you've got ten or twenty of those little bottles with scunge in the bottom, it would be worth it, but a single bottle, just sit tight on it.