Duralumin is an alloy of aluminum containing traces of copper, magnesium, and/or manganese. (It was revealed early in Mistborn: The Well of Ascension that the safe alloy of duralumin for Mistborn contains 96% aluminum and 4% copper.)
"A Mistborn that burns duralumin causes a reaction with any of the other metals they are currently burning to create an exceptionally large flare of the metal, consuming the remaining supply dry"
The exact degree to which duralumin enhances the next metal burned is unknown but appears to be massive: burning duralumin-enhanced pewter, Vin has exploded an assassin's skull with a hard head butt and later, with a single sword stroke, cut Straff Venture in half along with the horse he was sitting on at the time. Burning steel and pewter simultaneously, she was able to launch herself with tremendous speed over an open field, with more than enough time to refill on metals on the way back down.
A
Misting who can only burn duralumin is known as a "Duralumin Gnat"[1] as they gain no discernible effect from burning their metal.