The cork in a very old bottle of Vintage Port can sometimes become soft and difficult to remove with a corkscrew. To avoid having to draw the cork, Port tongs are sometimes used to remove the top of the neck of the bottle. The tongs, whose pincers are designed to grip the neck of the bottle, are first heated to a very high temperature over a strong flame or in the embers of a fire. They are then clamped around the neck of the bottle for half a minute or so while they transmit their intense heat to the glass. As soon as the tongs are removed, a cold damp cloth is wrapped around the neck. The sharp change in temperature causes a clean break to occur in the glass and the top of the neck separates from the bottle, cork and all.
To see this in action is quite a spectacle