PIGMENTS 153
refractive index is high but it is only slightly birefracting. Chemically, red lead is
fairly active. It is turned brown rapidly by nitric or acetic acid, which is the result
of the formation of brown lead dioxide; hydrochloric acid turns it white (lead
chloride); sulphides and hydrogen sulphide blacken it; it is not affected by dilute
alkalis. When exposed to light and air, it is not a particularly stable pigment
and has had, for centuries, a poor reputation in that respect. Red lead will turn
chocolate brown in color when exposed to either strong or diffuse light over a
period of centuries, particularly when it has been applied in a water color or
tempera medium. This darkening has been particularly noticeable on the wall
paintings of China and Central Asia. Gettens observed the phenomenon on the
wall paintings of Kizil in Chinese Turkestan (V-VIII centuries, A.D.), and the
strange, chocolate-colored faces on wall paintings at Tun Huang appear to add
further evidence. In films prepared from a glue medium, the darkening can be
produced artificially by exposure to light and high humidity, and seems to come
from the formation of brown lead dioxide. This fault of red lead was mentioned by
Cennino Cennini (see Thompson, The Craftsman's Handbook^ p. 25), who says
that it is good for painting on panel, but on the wall * it soon turns black, on
exposure to air and loses its color' (see Thompson, loc. cit.}. Red lead in oil, when
strongly exposed out-of-doors, may eventually turn pink or white because of the
formation of lead carbonate (white lead).
Red lead was a pigment of antiquity and was probably known as early as lead
itself. Lucas holds, however (pp. 290 and 308), that it was not used in Egypt until
Graeco-Roman times. By early classical writers, it seems to be confused with
other reds, particularly cinnabar or mercuric sulphide. Pliny describes it under the
name, secondarium minium (see Bailey, 1,119, 123, 217, 220-221), but appears to
have recognized it as distinct from minium, which was the name he used for
cinnabar or mercuric sulphide. The name, minium, came to be applied to red lead,
rather than to cinnabar, at some time in the Middle Ages.
Red lead is often found as a pigment on objects that date from antiquity.
Davy (p. 101) identified it as the orange-red on a vase at the Baths of Titus.
Laurie (* The Materials in Persian Miniatures') says it was a favorite with the
Byzantine and Persian illuminators. Thompson (The Materials of Medieval
Painting, p. 101) records that orange lead was common all through the Middle
Ages in manuscript embellishments and in painting, but that it was not used on
walls and not much on panels. This is in agreement with the negative findings for
red lead by De Wild on the Dutch and Flemish paintings he examined. It has been
identified, however, as a pigment on one of the panels of the Monte Oliveto altar-
piece, by Spinello Aretino (XIV century) in the Fogg Art Museum. It was widely
used on wall paintings in China and Central Asia, as has already been indicated.
In spite of its bright color and good covering power, artists do not much use it now,
although it is still obtainable in water color form. Commercially, however, it is