Andrew Birkett's nobugs.org
Duh, it would appear that my pan was the only aluminium one in a shelf full of steel pans. It had a polished exterior which made it look much like the steel pans. And I never stopped to double-check before sticking it in the furnace … I switched off the blower and plucked the big bits of the pan out of the furnace with visegrips (and wearing welding gloves). Oops.