The removal of wax preservatives applied as a matter of policy in the 19th century to medieval wall paintings, the repair of the rendering and the sympathetic reintegration of the murals within their architectural context are the most widespread problems in their conservation. Typical examples are given and illustrated. An appendix contains ten recipes for wax preservatives and the text indicates that they included instructions for their application, information which may prove relevant for current conservation. The products were supposed not only to act as consolidants, but also to enhance colors and control the glossiness of the surface. Ease of cleaning was one of the virtues claimed. But wax is damaging in ways spelled out in this paper, and moreover is not reversible. The practice of applying it ceased in the 1950's.