SUPPORTS 237
the ultimate fibre is only I to 5 mm. long, and has a large lumen and thin walls.
The tensile strength and wearing qualities are poor. The fibre contains much
lignin and has not good keeping quality. It is made into sackcloth and as such has
found occasional use as a paint support.
Larch (Larix). The common larch (£. europaea), a conifer3 is a native of
Europe and Asia. The North American representatives, L. laridna (tamarack)
and L, occidentalism are similar. The wood is coarse in texture and tough but,
unless carefully seasoned, it is liable to warp and bend; it is heavy and straight-
grained. The color of the heart-wood is russet to reddish brown. The annual rings
are distinct. In longitudinal section there are no characteristic figure or ray
markings. Although it is a tree well known in Europe, records do not show that
it was extensively used in panel painting except for a small number by the
German schools.
Leather (see also Parchment). This material is made from the skins of various
animals. These are prepared by a process known as £ tanning ' and are so rendered
flexible and imputrescible. (Raw skins, being subject to bacteriological as well as
chemical disintegration, readily putrefy.) The chief ingredient of tanning sub-
stances is tannin or tannic acid, secreted by various parts of a large number of
plants, and these are usually classified as Pyrogallols^ including chestnut, oak,
sumach, and others, and Catechohy including hemlock, mangrove, larch, birch,
and others. Oak-bark (Quercus robur) and Vaolnia (Quercus aegilops) contain
both types and, because'of the blend, produce excellent leathers. The fibres of the
plants are crushed and are then leached by infusion with water to produce a tan
liquor. (Under modern methods of manufacture this liquor is then tested for its
tannin content and for its acidity.) The skins or hides are cleaned and softened and
have the hair and the scarf skin or epidermis removed. The latter process is
usually one of liming and scraping. Lime, so used, is removed by washing the skins
in weak acid solutions. After that they are hung in successively different strengths
of tan liquor. When tanning and drying are finished, the leather is usually treated
with oils and is pared and smoothed, a process known as * currying.'
Although the tanning of leather is a craft which appears to be very old, the
product has never been in great favor as a support for paint. The reasons for this
are obvious and are both technical and economic. Leather did, however, figure
among the properties of interior decoration as well as for personal adornment and
for numerous accessories of dress and equipment. Paint was used frequently in
the designs laid on such objects. Painted leather harness is often found and a
Roman parade shield covered with leather on which are painted representations
has been discovered at Dura-Europos in Syria. Stamping and gilding leather was
an old craft in the Venetian lagoon and work of this order spread into other re-
gions of Europe. The Mediterranean basin seems to have remained the principal
source, however, of European leather in the middle ages, much of it coming from
the countries of the Moors and Saracens in Africa, or from Cordova, or Marseilles.