Coating was done with 3 layers of scotch #500 tape and 12% gelatin, i think it is something like 110 microns wet thickness total. Then i've dried for 6 hours and dipped for 1 minutes into 2.4% potassium alum solution, then 30 seconds in water and 1 minute in 4% FAC solution, then dried again for 8 hours at 50..60% humidity. I've included one more bath in potassium alum after developing (as i wasn't able to re-process first hologram in the batch again without damaging it), but not sure if that was really neccessary.
Well, i don't want to mess with chromium stuff and potassium alum does quite good, so i'll try to decrease its concetration in emulsion just. Anyway, i've found that i can mix both H2O2 developer and potassium alum solution (and both chemicals keeps their properties in the mix - i've got hologram fully developed in that), so the emulsion gets hardened right during developing, much like dichromated gelatin does during exposure. Perhaps i won't need pre-hardening even.For hardening gelatin, my preferred method is using chrome alum. I don't know if this is compatible with your ferric system, though. For example, one of my batches was mixed as follows: 0.5ml of a 5% chrome alum solution added to 47ml (room temperature) water, then 6 grams gelatin mixed into this and allowed to soak a while, then temperature raised to 44C.