Best way to clean up old Magnaite cookware?

SOS pad, that shite will be shining when u get done with it.

Use cream of tartar and a green scotch pad. Dampen, dust with cream of tartar and scrub scrub scrub.

Take it to the car wash and soak it down with the engine degreaser options. Then spray it with the power washer.

Barkeeper's Friend or Bon Ami and a brillo pad.

I've also actually heard that Oven cleaner works well and doesn't take as much effort, but you might do that outside because of the fumes.