Information from the Getty AAT
Heavy, opaque, orange-red pigment composed of lead tetroxide. Although chemically equivalent to the mineral minium, red lead pigment has been synthetically prepared by roasting lead white (480 C) since before the 5th century BCE. Red lead has been found as a pigment on early objects from Egypt, China, Japan, India, Persia, and Rome; it is no longer used as an artist's color because is has poor light stability and poor working properties, although it is still used to color glass and ceramic glazes. Pliny called it "secondarium minium." It was widely used in illuminated manuscripts, and with its use, the term "miniare" came to mean "to color with red lead," giving rise to the term "miniature." Red lead paint was used as an anticorrosion primer for structural iron and steel until the late 20th century.