UNKNOWN

[1908 p.38 in 1915 edition [entered as a separate recipe]: "The stability of pictures painting on canvas is enhanced if the back be protected by a metallic coating, so as to protect it in a measure, on that side at least, from the inroads of oxygen. The simplest way to secure this result is by coating the back with tinfoil, using to fix the metal in position a strong solution of shellac*. in spirits of wine. In order to guard against the penetration of oxygen through the accidental holes occuring in the tinfoil, a second sheet of this metal may be added when the shellac solution has become dry. This treatment may be applied generally to pictures painted on canvas, and virtually doubles their span of life. But protection from mechanical injury is not ensured by a thin coating of tinfoil. If that further protection be desired the back of the painting may be lined with sheet metal. According to the size of the picture, sheet copper or brass, or even sheet iron coated with tin or zinc, may be employed. Paintings executed on canvas may be fastened to the sheet of metal by the shellac* cement before named or with thick amber varnish. Thus the back becomes protected both chemically and mechanically by the same contrivance, and a high degree of durability is thus assured for the picture. "[continues to recommend sheet aluminium as a painting ground,and linoleum] ,*Perhaps marouflage is preferable.,