Prefixed ingots can be created from melted iron armor
Prefixed ingots can be created from fire bolted iron armor.
Problem
When "Something on the floor melts down into a puddle of metal!", due to fire bolting armor on the floor, prefixed ingots are created. This leads to odd items like "rotting iron ingot" or "vigilant iron ingot".
How to reproduce it
Drop iron body armors with a prefix (vigilant scale mail, rotting chain mail) on the floor. Then, cast Fire Bolt or zap a wand of fire at those until you see the "puddle of metal" message: it may take many attempts and there's always a chance of them being destroyed instead of turned into an ingot. When you manage that, pick the ingot(s) up and identify if necessary - then check their descriptions.
Notes
Suffixes can also be transmitted to ingots in this fashion. The game does not display them, but Greater Identify will tell you, leading to further zaniness - such as ingots that try to convert me to the forces of Chaos :D
I have no idea whether ego ingots operate normally for Smithing or not.
I've read reports of the weaponsmith's level 6 class power being able to do the same, and with weapons, but I don't remember whether I couldn't reproduce that or tried it at all. Can anyone confirm it?