Dog-eared' corners of pages and creases in paper are vulnerable areas which become brittle and easily tear or break. Lining', or the backing or an entire flat paper item with a reinforcing paper or tissue, is sometimes carried out on especially deteriorated or damaged works. Paper items are flattened in a variety of ways, depending on the strength and type of materials involved. Thick felts, boards and presses are usually employed. Large items such as heavy manuscripts are flattened for up to several weeks.
Leather dries out and deteriorates due to environmental and chemical causes.
In the past, book leather whether in poor or sound condition has been regularly treated with 'leather dressing'. Red rot is a common form of chemical decay in vegetable-tanned leather causing eventual disintegration into red powder. Depending on the degree to which red rot is present, it can be treated by painting on dilute solutions of cellulose ether adhesives and solvents. Leather dressings and red rot treatments should be only be used in consultation with a conservator. A substantial amount of deterioration and damage is caused or partly caused by contact with poor-quality materials.