supports	229
ology, Toronto), and the practice must have preceded that by many centuries.
Examples of it are found in Egypt dating from the early years of the Christian
era. A few scrolls from Chinese Turkestan (see Sir Aurel Stein, Serindia [Oxford:
Clarendon Press, 1921]) are from the Six Dynasties (265-581 A.D.). In the Far
East fabric was used with steady continuity by painters and, although important
paintings in Europe do not mark its employment so regularly, there is no reason
to suppose that it was ever abandoned. Pliny (XXXV, 51) remarks that the Em-
peror Nero ordered a colossal portrait of himself, 120 feet in length, to be painted
on canvas. The icon, the altarpiece, and walls of churches took precedence in
Christian painting, but linen and some silk were probably always used for painted
banners and for other purposes. In the third book of Eraclius, De Colorlbus et
Artibus Romanorum, chap, XXVI, are directions for preparing linen that is to be
painted on (Merrifield, I, 230). This was written in the XII or XIII century.
Cennino Cennini about 200 years later gives a similar but far more explicit
instruction (Thompson, pp. 103—104).
With the decline of painters' work on altarpieces and with pictures acquiring
larger scale, during the Renaissance, fabric or canvas was more and more used.
It is today the principal support for paintings executed in the oil medium. The
usual practice is to stretch the fabric on frames to which it is attached by tacks
at the outer edges. Most modern frames, called stretchers, are so mortised at the
corners that they can be slightly extended in outside dimension, and the fabric
tightened, by means of small wedges, called e keys,* inserted in the joint. Such a
stretcher is not much seen before the XIX century. Earlier than that, also, it was
the common practice to stretch the fabric before it was sized or had a ground film
applied. Now artists' canvas is bought in pieces or rolls ready for painting. In
consequence, these latter canvases show a ground film where they run over the
edges of the stretchers. In older paintings the fabric is apt to show no coating at the
edge. Usually linen or cotton has been used alone but there was an old, and very
sound, practice of using it over wooden panels. It was glued directly to the wood
and had a gesso ground laid over it. Probably this originated in Egypt and it was
much followed in Italy during the XIII to XV centuries. Occasionally it has been
combined with paper into a double support, the paper being used actually in
place of a ground film.
Fabrics, conservation and treatment. The deterioration of fabrics is largely
that of the cellulose which, except for silk, chiefly composes them (see Fibrous
Substances). To some extent this is an inevitable consequence of exposure to a
normal atmosphere. It has been found, however, that cellulose itself is extremely
resistant. Probably the principal deterioration of artists* canvas comes either
from materials that are added in the paint structures or from conditions that could
be avoided in the environment of a picture. Oil in the ground or applied at the
reverse of a fabric is one cause of its weakening. Not only does the oil film em-
brittle the whole structure; it also tends by its own oxidation to increase that of