he colors, ground finely with
linseed oil, were applied, according to the advice of Theophilus, in not
less than three successive coats, and finally protected with amber or
sandarac varnish: each coat of color being carefully dried by the aid of
heat or in the sun before a second was applied, and the entire work
before varnishing. The practice of carefully drying each coat was
continued in the best periods of art, but the necessity of exposure to
the sun intimated by Theophilus appears to have arisen only from his
careless preparation of the linseed oil, and ignorance of a proper
drying medium. Consequent on this necessity is the restriction in
Theophilus, St. Audemar, and in the British Museum MS., of oil-painting
to wooden surfaces, because movable panels could be dried in the sun;
while, for walls, the colors are to be mixed with water, wine, gum, or
the usual tempera vehicles, egg and fig-tree juice; white lead and
verdigris, themselves dryers, being the only pigments which could be
mixed with oil for walls. But the MS. of Eraclius and the records of our
English cathedrals imply no such absolute restriction. They mention the
employment of oil for the painting or varnishing of columns and interior
walls, and in quantity very remarkable. Among the entries relating to
St. Stephen's chapel, occur--"For 19 flagons of painter's oil, at 3_s._
4_d._ the flagon, 43_s._ 4_d._" (It might be as well, in the next
edition, to correct the copyist's reverse of the position of the X and
L, lest it should be thought that the principles of the science of
arithmetic have been progressive, as well as those of art.) And
presently afterwards, in May of the same year, "to John de Hennay, for
_seventy_ flagons and a half of painter's oil for the painting of the
same chapel, at 20_d._ the flagon, 117_s._ 6_d._" The expression
"painter's oil" seems to imply more careful preparation than that
directed by Theophilus, probably purification from its mucilage in the
sun; but artificial heat was certainly employed to assist the drying,
and after reading of flagons supplied by the score, we can hardly be
surprised at finding charcoal furnished by the cartload--see an entry
relating to the Painted Chamber. In one MS. of Eraclius, however, a
distinct description of a drying oil in the modern sense, occurs, white
lead and lime being added, and the oil thickened by exposure to the sun,
as was the universal practice in Italy.

113. Such was the system of