I have a 60-year old aluminum skillet that has spent most of those years in use atop a conventional electric burner. As a result, it has an uneven layer of crud fused to the bottom surface that I’d like to remove. This only recently became a concern because our new electric stove is a glass cooktop and this skillet won’t sit flat on its surface as is. Nothing that I have tried so far including steel wool has helped. Any ideas on how to remove, other than maybe some kind of power sander or an acid bath?