128 PAINTING MATERIALS
eye paint as early as predynastic times (see Lucas, p. 287). It was found side by
side with azurite in Chinese painting at Tun Huang and other temple sites, and
it has perhaps been used in the East continuously to the present day. This copper
green is found in all periods of European painting up to about 1800, but at that
time it was nearly supplanted by artificial green pigments. It was used much in
trees and foliage. Like azurite, it worked better in tempera than in oil. Thompson
remarks (The Materials of Medieval Painting, pp. 160-162) that malachite, al-
though widely used in the Middle Ages, is mentioned but little in contemporary
literature on painting materials whereas azurite is spoken of repeatedly. This
pigment is no doubt the verde azzurro of Cennino Cennini (see Thompson, The
Craftsman's Handbook, p. 31).
Manganese Blue is a comparatively new pigment which seems to have been
first mentioned in the patent literature about 1935. This green-blue pigment is
essentially barium manganate fixed on a barium sulphate base. It is made by
calcining mixtures of sodium sulphate, potassium permanganate, and barium
nitrate, or their equivalents, to a temperature of 750-800° C. in the presence of
air. The blue pigment formed is very inert chemically; it is unchanged by heat
and is insoluble in strong acids and alkalis. The pigment is fairly coarse and
somewhat irregular in particle size. Many rectangular particles with rounded
corners can be observed; they are moderately birefracting. Although weak in
tinctorial and in hiding power, this pigment may have special uses because of
its chemical stability. So far, it has been used almost exclusively for coloring
cement; it should be of interest to fresco painters. (See French patent 778,290,
March 13,1935, to I. G. Farbenindustrie A. G. [Chemical Abstracts, XXIX, 1935,
46io3]; French patent 802,687, September 10, 1936, to Wolfgang Mxihlberg
[Chemical Abstracts, XXXI, 1937, 2O295]; British patent 465,912, May 19, 1937,
to Wolfgang Miihlberg [Chemical Abstracts, XXXI, 1937, 823O3]).
Manganese Violet (permanent violet) is said to be manganese ammonium
phosphate, (NH4)aMn2(P2O7)a (Rose, p. 255). In the method of preparation de-
scribed by Weber (p. 88), manganese dioxide and ammonium phosphate are
melted together, with the evolution of ammonia, and the fused violet mass is
digested with phosphoric acid and heated until a correct color is produced; the
product must be thoroughly washed free from phosphoric acid. Church (p. 225)
says that it has a truer violet hue than cobalt violet (cobalt phosphate) which is
redder as well as brighter. The pigment is permanent to light and is unaffected
by heat, but it is decomposed by strong acids and by alkalis, which makes it
unsuited for fresco. It is not much used by artists because it is dull in tone and
has poor Chiding power (see Doerner, p. 81). The manganese violet described
by Merwin (p. 521) was birefracting and belonged, probably, to the orthorhom-
bic system. Little is known apparently about the history of this pigment, except
for abatement by Messrs Winsor and Newton in their catalogue (1930 ed., p. 18)
that it was first introduced by them in 1890. It is understood, however, to have