Complete the account of the layers under the paint.

The traditional sealing layer between fabric and ground is rabbit-skin glue, commonly made at about seven per cent by weight in water. A frame whose corners can be driven apart to re-tension the cloth is a stretcher, while a fixed one is a strainer. The thin toned layer laid over the ground before painting is the imprimatura. Cotton duck is more hygroscopic than linen and therefore slackens and tightens with the weather.

The second blank is a distinction worth keeping. Every canvas slackens eventually, and a strainer offers no way to answer that except restretching the whole picture, which is why a strainer is a decision about the next fifty years disguised as a saving of a few euros.