Red Lead is produced by raising massicot (the commercial name for oxide of lead) to a high temperature, short of fusion, during which it absorbs oxygen from the air, and is converted into red lead or minium, an oxide of lead.

It is usually in the form of a bright red powder. Ground by itself in oil or varnish, it is durable and unaffected by light when the red lead is pure and used alone, but any preparation containing lead, or metallic salts mixed with it, deprive it of colour, and impure air makes it black.

Uses

Red lead is used as a drier (see p. 412), also for painting iron (see p. 336); and in the priming coat for painting wood (see p. 419).

Adulteration And Tests

Red lead is sometimes adulterated with brick dust, which may be detected by heating the red lead in a crucible, and treating it with dilute nitric acid; the lead will be dissolved, but the brick dust will remain.2

Red lead may also be adulterated with colcothar, a sesquioxide of iron.

Antimony Vermilion, Sulphide of Antimony, produced from antimony ore, has been proposed as a substitute for red lead.

It is sold in a very fine powder, without taste or smell, and which is insoluble in water, alcohol, or essential oils.

It is but little acted upon by acids, and is stated to be unaffected by air or light It is adapted for mixing with white lead, and affords an intensely bright colour when ground in oil.3

1 Ure.

2 Davidson.

3 Proceedings Society of Engineers, 1875.