Hide glue (or rabbit skin glue) has been used for many centuries to ‘size’ canvas before it is painted on. Coating the canvas in thin layers of warm glue seals the fibres, reducing absorbency and creating a barrier between the canvas and the oil in the paint, which would otherwise soak in and leave too little oil in the paint on the surface.

Hide glue is a very powerful glue and will shrink a canvas substantially, causing it to tighten over its stretchers. If the glue is too strong, the tight canvas can warp the stretchers, or the fibres can break, causing the canvas to slacken again.