The lining of paintings is a process of restoration used to strengthen, flatten or consolidate oil or tempera paintings on canvas by attaching a new canvas to the back of the existing one. The process is sometimes referred to as relining. In cases of extreme decay, the original canvas may be completely removed and replaced.
The purpose of lining a painting is to flatten or consolidate its surface or strengthen its support by attaching a new canvas to the back of the existing one. The process has sometimes been referred to as relining. In cases of extreme decay, the original layer canvas may be completely removed, and the new canvas fixed to the priming on the reverse of the paint layer.
Lining has been very widely practiced, and during the 19th century, some painters had their works lined immediately after, or sometimes even before, completion. There have been some doubts concerning its benefits more recently, especially since the Greenwich Comparative Lining Conference of 1974.
The procedure as carried out in the 19th century is described by Theodore Henry Fielding in his Knowledge and Restoration of Old Paintings (1847). The picture was removed from the stretcher and laid on a flat surface. The edges of the canvas were trimmed, leaving the original support smaller than the new lining. A sheet of paper covered in thin paste was laid on the surface of the painting, which was then placed face-down on a board or table. The back of the picture was then coated with paste, copal varnish, or a glue made from cheese. The new lining canvas was pressed down onto the back of the picture by hand; then the outer edges of the lining cloth were fastened to the table by means of a large number of tacks, and a piece of wood with a rounded edge was passed over the back of the cloth, to ensure perfect adhesion. When the glue had dried sufficiently, the lining was smoothed with a moderately hot iron. Fielding cautions that "the greatest care must be taken that the hand does not stop for an instant, or the mark of the iron will be so impressed on the painting, that nothing can obliterate it." The picture was then nailed to a new stretcher, and the paper was washed off with a sponge and cold water.
Fielding also describes the process for the complete removal and replacement of the canvas. In this, the picture was covered with paper, as if for lining, then fastened to a board or table, after which the old cloth was rubbed away with a small rasp with very fine teeth; when the restorer had gone "as far as may be prudent", the remainder of the cloth could be taken off with a pumice stone, until the ground on which the picture was painted became visible. It was then ready to receive its new cloth, which had previously been covered with copal varnish, glue, or paste. In this procedure, the hot iron was not used.
The use of hand-ironing is liable to produce a flattening of impasto. This problem was mitigated by the introduction in the 1950s of vacuum hot-table processes, designed for use with wax-resin adhesives, which exerted a more even pressure on the paint surface; however the longer periods of heating and high temperatures involved often led to other types of textural alteration.
Wax-based adhesives seem to have been in use for lining from the 18th century, although the earliest well-documented case of their employment is in the lining of Rembrandt's Night Watch in 1851. Although, initially, pure beeswax was used, mixtures incorporating resins such as dammar and mastic, or balsams such as Venice turpentine, were soon found preferable. During the 20th century, it came to be realised that the impregnation of the paint layer with wax could have deleterious effects, including darkening of the picture, especially where canvas or ground were exposed.
Although experiments with synthetic fabrics were carried out during the 1960s and 1970s, traditional linen cloths are still usually used for lining. However polyester canvas is often used for strip-lining, where only the edges of the painting are backed, and for loose-lining, in which no adhesive is used. This latter technique helps protect the painting from atmospheric pollution, but does not flatten or consolidate the paint surface.