PIGMENTS 161
ilmenite (originally menachanite), was first described by an Englishman, the Rev.
William Gregor, as early as 1791, but the element was named < titanium ' by the
German chemist, Klaproth, in 1795 (see Weeks, pp. 142-146). Attempts were
made to develop it for pigment purposes early in this century (Rose, pp. 357-359),
but not until about 1916-1919, however, were certain companies in Norway and
America (see Toch, Chemistry and Technology of Paints, p. 48; also Trillich, III,
52) able to overcome difficulties in the purification and .manufacture of the oxide
and to put it on the market in regular production. The native oxide of titanium,
rutile, occurs in nature, but the titanated iron ore or ilmenite (FeTiOs), found in
large deposits on the west coast of Norway, today supplies the titanium of
commerce.
For the preparation of this pigment, the ilmenite ore is digested with con-
centrated sulphuric acid, and the coagulated mass of iron and titanium sulphate
which is formed is dissolved in water and then heated to boiling to precipitate the
titanium as metatitanic acid and separate it from the iron. The precipitate is
neutralized with barium carbonate and is then calcined. Commercially, only a
small amount of titanium dioxide is used, pure, as a pigment for white paints.
Most of it is sold as a composite in which it is precipitated on a base of barium or
calcium sulphate. Barium base titanium oxide is usually about 30 per cent titan-
ium oxide and 70 per cent barium sulphate. In the preparation of this composite,
the titanium sulphate is mixed with blanc fixe (artificial barium sulphate), and the
mass is boiled to precipitate titanium hydrate (metatitanic acid) upon the blanc
fixe.
Both the pure titanium and the barium base titanium oxides are micro-
crystalline and fine in texture. The high refractive index (a? = 2.5-2.6) and, hence,
the great hiding power, is the outstanding characteristic of titanium dioxide.
Beam (p. 58) says that, bulk for bulk, paints made with pure titanium white
have nearly twice the opacity or obscuring power of paint made with pure white
lead. The pigment is used extensively in inside white enamels and also as a
ceramic white.
Titanium dioxide is a very stable substance; it is unaffected by heat, by dilute
acids and alkalis, and by light and air. As a pigment, it is non-reactive with drying
oils and is a poor drier; hence, it gives soft paint films unless much zinc oxide or
drier is added. The oil absorption of pure titanium dioxide is fairly high, 23 to
25 per cent, but that of the barium base pigment is lower, 17 to 18 per cent (see
Gardner, pp. 1228-1229). Titanium oxide was suggested as an artist's pigment
very soon after it came into commercial production, and, for some years, titanium
barium pigments have been supplied under special names by various artists'
supply houses. One can not expect to find it used, however, on paintings that were
done much earlier than 1920.
Titanium White (see Titanium Dioxide).
Titanox (see Titanium Dioxide).