Cyanotype on glass (oxalic acid question)

Ive been reading through alot of forum posts and pages about cyanotype on glass. I plan on using the Photography Formulary A+B formula.. but alot of gelatin on glass recipes call for oxalic acid. (I believe its used to help harden the gelatin?) Is there something I can replace this with? Or a cheap place to get oxalic acid from? Or can the oxalic acid be omitted?

Thanks!

I think maybe it is used as a preservative for the cyanotype solution, rather than a gelatin hardener. But I haven't used it so I'm not sure.

Lots of discussion here