I learned a hard lesson about sorting metals before cleaning them. I put an old griddle into a lye bath thinking it was cast iron but it turned out to be aluminum. The lye completely ate the aluminum and left a nasty grey coating on my actual cast iron pieces. A regular scrub brush isn't touching this gunk. I am currently building an electrolysis tank to see if that pulls the residue off. If you are cleaning old cabin finds, double check them with a magnet first because aluminum won't stick. Has anyone else dealt with this specific type of lye reaction?