Smelting always works with fortress-produced items, but *sometimes* the job does not recognise melt-designated items left behind by goblin sieges as existing. I now have a stockpile near my smelters of copper and iron armour and weapons which are all melt-designated, but they have been there for years, and whenever I set a work order to melt metal objects, the jobs always cancel immediately.

Initially, I wondered whether the decoration on items was a factor. But even if it is, it is not the whole story, as I have both decorated and undecorated items that cannot be smelted.

It is not a stockpile issue; I have tried all combinations of linked/unlinked stockpiles and workshops.

Bizarrely, this is actually a problem specific to Magma Smelters. I built a regular smelter, gave it a 'Melt a metal object' task to loop indefinitely, and it very happily issued and completed jobs to melt all the stubborn melt-designated objects in my stockpile.