PAINTING MATERIALS
white used on easel paintings from remote antiquity to the XIX century. Radi-
ography of old paintings rests to a great extent upon the generous use of white
lead in the past: since lead has a high atomic weight, it has a high mass ab-
sorption coefficient for Roentgen rays (see De Wild, pp. 92-98). Its first use as
a paint pigment must have been very early. It is not mentioned extensively,
however, by either Partington or Lucas in their accounts of the materials of the
Egyptian and other early civilizations. It must have been used in classical times
for painting pictures as well as for cosmetic purposes. It has been identified as
a pigment on Fayum portraits (see George L. Stout, ' The Restoration of a
Fayum Portrait/ Technical Studies, I [1932.], p. 86), and was probably known and
used as a pigment in the Orient quite as early as in the West. It lies thickly on
painted sculpture of Tang times from Tun Huang in Western China. In Europe,
hardly an important painting, before the XIX century, is without it. De Wild
has listed (pp. 34-39) over 80 paintings in which it occuis.
Although white lead has been used in tempera and in water color, it is not so
satisfactory in these mediums as in oil. Today its place in water color has been
largely taken by zinc white (Chinese white), and in oil it is meeting serious com-
petition from the titanium pigments. The pigment is sold to the artist under the
name, * flake white/ Cheaper grades are sometimes ' cut' or adulterated with
barite or blanc fixe.
Cremnitz (Kremnitz) white is a special kind of white lead which is prepared
by the action of acetic acid and carbon dioxide on litharge. It is now greatly
favored by artists because it is considered to be whiter, denser, and more crystal-
line than ordinary, Dutch process white lead.
Whiting (see Chalk).
Woad is a blue dye very similar to indigo (see Indigo) which is obtained from
the leaves of the woad plant, Isatis tinctoria, a herbaceous biennial indigenous to
southern Europe. Before the importation of indigo in the XVII century, it was
widely cultivated in England and on the Continent for its dye (see J. B. Hurry,
The Woad Plant and its Dye [[London: Oxford University Press, 1930]), which
is extracted by a fermentation process similar to that used with indigo. Although
the coloring principle of woad was formerly thought to be the same as that of
indigo, it is now known to be a distinct substance (see Perkin and Everest, pp.
524-525). Woad blue was apparently used in mediaeval times for a pigment as
was indigo (see Thompson, The Materials of Medieval Painting, pp. 135-140).
It is quite impossible to distinguish between the two when they occur as pigments
in old paintings.
Yellow Berries (see Persian Berries Lake).
Yellow Lake (see Quercitron Lake).
Yellow Ochre (see Ochre).
Zinc Green (see Cobalt Green).
Zinc White (Chinese white), or zinc oxide (ZnO), has now almost the impor-