if the shellac will cause the storage cans to rust then will shellac cause your tools or other steel items to rust if they touch shellac ?
Nope - the shellac dries too fast for one thing and it also forms a nonpermeable film that won't allow rust to form.
It could be that water causes some form of acid to form in a can of shellac which corrodes the can.
John - possibly - but - I've seen cans that were unopened build up pressure and the lids and bottoms get domed shape.
They'd be sitting on the shelf right next to cans that were from the same mfg. lot that were fine.
It's puzzling at best.
It doesn't seem to matter either if the shellac is orange, blonde, dewaxed, ,,,,what pound cut it is or what age it is - although older cans that have been opened do seem a bit more susceptible - but - I've seen fairly fresh cans blow their lids also.
My solution to the problem is to stick the cans I use in a plastic bucket & drape a towel over the top.
"Life is what happens to you while you're busy making other plans." - John Lennon