Please note that "grocery store" alum is likely to contain flow/anti-clumping agents which make it a no-no for emulsion work. As a hardening bath during processing, K alum works reasonably well, if given a bit of help with a strong acid.

Glutaraldehyde is a reasonable hardener for paper emulsions, but it is rather fast and touchy - turn your back on it and you might find your emulsion has turned into rubber btdt