62 PAINTING MATERIALS
Size (see also Gelatin, Glue, and Parchment Size) is a term frequently applied
to gelatin or to very pure glue. Herringham, in * Notes on Mediaeval Methods '
in her translation of the Book of the Art of Cennino Cennini (p. 243) says that,
except in English, there are not distinct words for size and glue, and the word,
* glue/ is constantly used in translating where c size' would be more nearly
correct. Church (p. 63) maintains that the term, ' size/ should be synonymous
with ' gelatin' derived from skins and bones. It should not be used for ordinary
glue, especially that from cartilages and sinews, which contains chondrin. It
has been a custom, however, to use the term more broadly for various materials,
like starches, gums, and albumen, that are used to stiffen fabrics and to give a
smooth surface to writing paper. In paper manufacture, much ' rosin size ' is used
for that purpose. In its broadest sense, the term, ' size,' is used to mean any
material that fills or dresses a porous surface. Glue size is frequently used in
preparing wood surfaces for painting. Thompson (The Practice of Tempera
Painting^ pp. 18-20) gives directions for the making and application of gelatin
size in the preparation of a panel for tempera painting.
Skin Glue is impure gelatin prepared from the skins of animals (see also
Gelatin and Glue).
Soap is any metallic salt of a fatty acid. Ordinary soap is the sodium salt but
soaps can also be formed by lead, manganese, cobalt, and other compounds
combining with fats and oils. When a fat or oil combines with a metallic hydroxide
to form a soap, glycerine is set free. (See Saponified Oils and p. 200.)
Sodium Silicate (see Water-Glass).
Soya Bean Oil. The soya bean (Glycine hispida and varieties) is native to
China, Manchuria, and Japan, and the plant is being cultivated in other countries.
The seeds contain about 18 per cent of oil. A typical analysis of soya bean oil
gives 14 per cent of palmitic acid, 26 per cent of oleic acid, 57 per cent of linoleic
acid, and 3 per cent of linolenic acid. It is a slow-drying oil (its iodine number is in
the neighborhood of 130), and it forms a soft and not very durable film. It is used
in some tube colors to meet the demands of the painter for more slow-drying
colors. (See also Oils and Fats.)
Spermaceti (see also Waxes) is obtained as a solid precipitate from the head
oil of the sperm and bottlenose whales (Physeter and Hyperoodon). It occurs in
glistening, white, crystalline masses and is very brittle.
Spirits of Turpentine (see Turpentine) is the distillate of crude turpentine or
balsam. The balsam collected from conifers is allowed to settle and spirits of
turpentine is distilled off, leaving the residue, colophony or rosin. The word,
* turpentine/ is now commonly used instead of the longer term.
Spirit Varnish, a resin dissolved in a volatile solvent (see Varnish).
Stand Oil. According to J. G. Beam (The Chemistry of Paints, Pigments and
Varnishes [London: Ernest Benn, Ltd, 1923], p. 226), * stand oil' is derived from
the German word, Standole. This gets its name from the fact that, on standing,