The lining is the process of glueing a new canvas on the backside of the original one. Two different methods with the same result exist.
The traditional way is carried out with the use of a natural rabbit-skin glue, water and heat.
A more recent way is by using a synthetic and thermoplastic adhesive which permits the « sealing » of both canvases. The main part of this process happens on a heated vacuum table.
Since lining is a drastic, long and traumatic operation, it is one of the last resorts of the restorer.