Most period armour was maintained by squires or grooms who would go over the surfaces with a brush. More extensive work was probably done at a guildhall, where waterwheels could be used and coated with fine sand to act as sandpaper. Similar wheels covered in
leather and painted with various compounds could easily polish armour in the same way that we can do now, but at a much slower pace.
Mail was often placed into drums and dragged or turned, tumbling it with sand and vinegar to remove the rust. I can find no authentic references to the use of wax or oil in the care of pieces.