PAINTING MATERIALS
the fibre and to change it to oxycellulose. Glues or pastes used in priming encour-
age the growth of mold and micro-organisms which will attack and destroy the
fabric. They can be kept from growing by conditions in the rooms where paintings
are put. Darkness and dampness (a relative humidity of 65 per cent or more) are
all that such organisms need to start their development in a normal room temper-
ature. Spores are almost sure to be present.
Treatment of the fabrics used for paint supports may include attempts at
disinfection to remove active micro-organisms. Such treatment is usually made
with thymol vapor or formaldehyde applied either in solution or in closed cham-
bers. By far the most usual treatment, however, is that known as * relining.'
The aim of this is to strengthen the fabric structurally. It is a process of backing
the old canvas with a new one, a film of adhesive material being used to attach the
two. In general, this treatment has been applied for at least 200 years. In its
application usually a light facing is attached to the paint and often this is held on
a stretching frame. The old canvas being removed from its stretcher, it is carefully
cleaned and smoothed on the reverse side. A new canvas is selected, stretched,
and sized or impregnated. The old canvas is sized or impregnated also, enough
of the adhesive material being left to form a bond. The two surfaces are then set
together and the adhesion is established usually with heat and pressure.
Until the late years of the XIX century, the principal adhesive for the relining
process was glue. It was sometimes used in emulsions with oils or varnishes. Then
wax and a mixture of wax with a small amount of resin came into use and has
sometimes been called the 'Dutch process * of relining. Wax has found much favor.
The general technique is not very different but impregnation of the old fabric is
more certain and the sealing power against dampness is, of course, far greater than
that of glue. Glue also suffers from, its tendency to augment the growth of mold.
Mounting instead of relining has occasionally been done for European paint-
ings on fabric. In this treatment the principle is much the same but a rigid panel
instead of another fabric is used at the back of the old support. For the most part,
the wax type of adhesive is used, and the development of this and of artificial
boards has greatly encouraged adoption of the method for use with small
paintings. In the East, of course, mounting has been practiced for many centuries
and is used for paintings on silk or paper. It is done largely with paste as an
adhesive.
Fibrous Substances* Fibres are special structural components of animal and
vegetable origin which are utilized in textile, paper, cordage, and brush manu-
facture. Only one important fibre, asbestos, is of mineral origin; it is no special
structural component like the animal and vegetable fibres but is an unusual
crystalline form of a mineral substance.
Animal fibres are composed of nitrogenous colloids like the albumins, fibrins,
and gelatins and they are of highly complex constitution. Unlike the vegetable
or cellulose fibres, they are resolved and finally dissolved by alkalis whereas the