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I've read up on a few bluing formulas and most called for potassium nitrate, some used ammonium nitrate because of availability but the process had to be done outdoors due to ammonia fumes, any nitrate salt will do the job, and I'm sure sodium nitrate will work but potassium nitrate, being non hygroscopic and non fuming, is more stable in the formula compared to sodium/ammonium nitrate.
Hope this helps
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so once the hot tank has been made, and the solution used, is there any special storage requirements?
I recall we had a hot bluing tank in SHS, and the teacher just kept a lid on it most of the year, but I never knew if there was fumes causing corrosion, or if the mix had to be dumped each year, etc.
I imagine the salts would need to be renewed/ added to over time, but if the tank was only used once every 3-6 months, is there any storage considerations needed?
FYI - been a while since I bought potassium nitrate - but the hydroponics people seem to have good quality fertilizers at reasonable prices...