ferric oxalate questions
I understand Ferric Oxalate deteriorates over time.
What is the expected shelf life?
If I use "stale" ferric oxalate, how will the image look?
Can it be extended by refrigeration if a few days/weeks inactivity is expected?
Finally, what is the impact of the addition of potassium chlorate as a "restrainer" in the B&S 2 solution? Does it make the resulting positive image more contrasty or less?
I was concerned about this and spoke with the guys at B&S a couple of months ago and they advised that THEIR ferric oxalate has a pretty long shelf life (their process is apparently proprietary/patented). I was told to expect in excess of 1 year. I have been using some that I have had for 6-8 months and it's still fine. Evidently the images start to look muddy with reduced contrast. I have yet to experience it with their product.
I tend to buy a couple of bottle at a time and stash one in the fridge. I try not to have one opened for more than a few months (up to six), and I don't worry about the age of the refridgerated one. But if I am not sure about the age and/or condition, I don't use it. The stuff is too cheap to take a chance of wasting platinum and palladium salts. I tend to coat 6 to 10 8x10 sheets at one time and then print until I use them all, so it is not worth my time to coat just one sheet for a test (I have to travel up to where I print...10 miles away...pull out and set up trays, chemicals, equipment, etc).
If I remember correctly, the print tends to get more contrasty with older FO. However, an easy way to rejuvenate an FO solution is to add a few drops of hydrogen peroxide. This reliably changes the ferrous oxalate back to ferric. I do this routinely when I pick up an older bottle I haven't used for some months.
One thing to remember is that ferric oxalate is light sensitive. Keep it in the dark, as well as cool and (if powder) dry.