An unidentified tub of something can be:
A tub of lard
A tub of grease
Applying both tubs to armor and weapons makes them greased. Applying a tub of grease will identify it. It is unknown whether applying a tub of lard to food raises the nutritive content, though that would make sense. Greasing an item makes it resistant to acid and rust, but vulnerable to fire. Greasing a helmet will prevent its removal by a mindflayer.