The permanence of an oil painting depends largely on its own physical resources to withstand age and to withstand the repeated interventions of restorers. While many British paintings of the 18th century have deteriorated, most of those of the 17th century are stronger and more resistant. This note compares the formulation of some 17th-and 18th-century paints, and places emphasis on the changes which occurred to the vehicular components. The use of freshly made materials in the 17th century brought highly individual characteristics to the paint, affecting the artists' style, expression, and the permanence of their work. By the end of the next century these features had been lost, partly due to the commercial availability of prepared artists' paint, but mainly to the substitution of additives, such as megilp and other thickened oil varnishes. These changes brought increased risk of damage through cleaning to many paintings and led to the destruction of many fine works.