The Leaching of Linseed Oil Films in Iso-Propyl Alcohol

Abstract

MOST of the work so far published on the effects of solvents on aged linseed oil films has been done on model films prepared in the laboratory. Although such experiments permit studies on adequately characterized materials, the results are open to the criticism that they cannot be extrapolated to enable predictions of the behaviour of really old paint films. Such films from paintings upward of a hundred years old are sometimes asserted to be much less affected by cleaning solvents than films made in the laboratory (see, for example, re£ 4) and of necessity only a few years old. Unfortunately, it is almost impossible to find suitable samples from old paintings themselves for research purposes, since lnost works of art which have come down to the present day have been cleaned before, often many times, and their detailed case histories are not known. When films a few years old are immersed in solvents absorption of the solvent takes place causing the film to swell. This swelling facilitates the dissolution of a fraction of the filma process known as leaching. Both these phenomena have been discussed by Stolow [I] who published data on both pigmented and unpigmented films of linseed and stand oils supported on glass plates. He found that equilibrium solubilities for a range of solvents tended to converge to limiting values in the range of I6-32o/0 (by weight), though higher values were recorded. Picturing the dried linseed oil films as a randomized aggregate of polymeric units highly branched but only lightly cross-linked, Stolow was able to account for the n1ain features of the leaching and swelling behaviour, and a model of this kind proved to be reason-