I will be making ferric chloride in a jar...+100g of Iron (acquired from fine steel wool) +100ml Water +100ml Muriatic Acid (~32%) =~200ml of Ferrous Chloride +200ml of 3% Hydrogen Peroxide =~400ml of Ferric Chloride

Why? Well it's a compound that will harden gelatin when exposed to UV. More interestingly, you need an inhibitor to prevent premature hardening. So the inhibitor happens to be either Ferric ammonium citrate or oxalate, which I already have on hand.