Been trying to remove a rusted up cast iron plug. Been using plus gas by heating and soaking but using a hot air gun than a blow lamp. Have tried acetone as a soaking method to penetrate further. But rather than heat which can be destructive I wondered if anyone has freezed a plug nut or bolt just to break the rust seal so the penetrating oil can penetrate further. If I surrounded a base plug seized on a mills with plasticine and froze the the centre of the base plug with the plasticine protecting to avoid contact with the body using pipe freezer from a can that plumbers use to freeze pipes. In theory the base should contract and shrink, the opposite of heating the body which would expand. Do you think freezing would work to free up a rusted part to break the rust seal? If this did work that's if anyone has tried it then it would be a plus than using heat that could damage paint work and markings etc. What do you think.