I've been making my own paper fixing solution from bulk sodium thiosulfate and sodium sulfite for some time now. I love using the bulk raw chemistry as unlike commercial products I have no immediate concerns of it being suddenly discontinued. It's also super easy with only two components. The other great advantage is I only mix it up as needed, so the chemistry is always absolutely fresh and new.

The disadvantage with homemade chemistry is I don't have any solid information on time, dilutions, strengths or capacity. There are no handy package instructions.

Looking at the processing recommendations from various paper makers isn't necessarily useful. They all say to use their own brand of chemistry--and then the fixing times and dilutions vary among the manufacturers.

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So, for my homemade fix how can I go about finding or testing its limits myself? Of prime concern to me is the fixing time. I don't want to fix too short a time (30 seconds), nor do I want to unnecessarily fix too long (ten minutes) either. This will be for fiber-base paper.

I do want to find an adequate and well sorted processing regime for "archival" (an oxymoron) black and white printing. Going through the considerable time and expense of darkroom work and not following up on good processing is foolish.

Any suggestions for homemade fix?