Blasting
When wringing (also pushing ), two smooth, flat surfaces are only connected by their molecular forces of attraction . To do this, they must be free of dust, grease or other contamination; to do this, they are cleaned with tetrachlorethylene, for example . Wringing can be used to hold glasses while they are being processed or to join multiple gauge blocks together . After some time, cracked metals can no longer be separated by cold welding .