Salem

So I filled up my smelter and activated it b4 i went to sleep and In the morning there was only 11 dross in it(I put 13 ore so there are 2 empty spaces)
I highly doubt it was robbed because I had iron in boxes in front of the smelter and even more valuable stuff...
does it disappear sometimes over a long period of time or something?

I regularly just leave iron in smelters for days, never seen it go poof, if its gone its been taken. Might try to look for scents to confirm.