The ratio of oil to resin in a medium. For an oleoresinous varnish, the oil length may be expressed
in terms of parts by weight of oil to one part by weight of resin. However, in American practice, it
is common to express oil length in terms of U.S. gallons of oil per 100 pounds of resin. Thus, in
American usage, a 25-gallon varnish would be a varnish composed of 25 U.S. gallons of oil to
100 pounds of resin. For an alkyd resin, oil length is expressed as the percentage of oil by weight
in the resin.