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? Thanks.