MEDIUMS AND ADHESIVES 71
of purple, they put on caeruhum as the ground colour, and then lay on purpurissum
with egg.
The translator, (op. cit., pp. 68-69) says that gum, egg, and glue were all at the
command of the classical painter and refers, also, to a mention, in a papyrus of
Thebes, of a medium made of egg and gum to which was added bile, to make the
color flow easily.
The mixture of egg white and gum was evidently common at later times.
Cennino Cennini (c 1400) speaks of it (Thompson, The Craftsman'j Handbook^
p. 102) as a medium for c mosaic gold * and it appears in the Naples MS. of the
late XIV century (Thompson and Hamilton). Occasional strange mixtures of
tempera for paint are found in treatises on materials that reflect medieval practice.
Among these are two in the MSS of Jehan le Begue. One (Merrifield, I, 306) is
made of lime, ashes, wax, fish glue, and mastic. Another (Merrifield, I, 316) is
made of pieces of flesh boiled in water with the root of the plant called,' stipatum*
Gums and glues (including size) must have been used extensively in European
tempera besides their employment in illumination. Gums, particularly, are often
mentioned in the Strasbourg MS, (Berger, III, 155 ff.). Yet it is probable that
egg was the common tempera of European paint during the Middle Ages and the
early Renaissance. It also, either as glair or whole egg, is frequently mentioned in
the Strasbourg MS., a document of the XV century and definitely northern in
origin, and it is clearly the main tempera medium treated by Cennino Cennini,
the chief recorder of Italian practice. For panel painting this writer prescribes the
yolk alone (Thompson, The Craftsman's Handbook, p. 91):* . - - you must always
temper your colors with yolk of egg, and get them tempered thoroughly—always
as much yolk as the color you are tempering.'
Analysis of paint from a portrait by Holbein (unpublished report by Ruther-
ford J. Gettens) indicated that the medium was tempera. It is probable, however,
that egg tempera did not long survive in general practice after the XVI century.
By certain slight changes the transparent inks and thin gum temperas used in
connection with writing, drawing, and illuminating were ultimately worked into
a standard paint having a medium of gum with additions of hygroscopic materials.
This paint, called ' water color/ is very common in present-day practice and is
used thinly on a support of paper (see Gums).
Tung Oil, also called' Chinese wood oil,' is obtained from the seeds of Aleurites
cordata, A. fordii, and A. montana, contained in a nut, and growing in China
and surrounding countries. A similar tree is native to Japan and yields Japanese
tung oil which varies slightly from the Chinese oil and is not so satisfactory. The
seeds contain about 50 per cent of oil. The native method for separating it is very
crude. The seeds are roasted over a naked flame and are ground between stones
before expression. Wooden presses are used. The cold-pressed oil is light in color
and is mainly exported; the hot-pressed oil has a very dark color. The former is