126 PAINTING MATERIALS
a purplish blue solution which changes to brown on exposure to air. Brown,
reddish brown, black, and blue-black lakes can be prepared from logwood ex-
tracts with various mordants. All are insoluble in water and alcohol, are turned
bluish violet by alkalis, and are decomposed by mineral acids with the formation
of a blood-red solution. Logwood extract (as haematoxylin) is widely used as a
biological stain. When treated with bichromate, it was formerly used in the
manufacture of writing inks. Extracts were used, also, in dyeing and in the lakes
for water colors, but, because they are fugitive in strong light, they have been
discarded.
Madder, Madder Lake (see also Alizarin), is a natural dyes tuff from the root
of the herbaceous perennial, Rubia tmctorium^ which formerly was cultivated
extensively in Europe and in Asia Minor. Roots from plants 18 to 28 months old
grown in a calcareous soil are best. The coloring matter, which is chiefly alizarin,
or 1,2 dihydroxyanthraquinone (C^HsC^), is extracted from the ground root by
fermentation and hydrolysis with dilute sulphuric acid. The madder plant is
native to Greece and was used as a source of dye perhaps as early as classical
times (Church, p. 171). It is understood to be the rubia of Pliny (see Bailey, I,
37) and other classical writers. It has been identified as the source of a pink color
on a gypsum base from an Egyptian tomb painting of the Graeco-Roman period.
There are specimens of it in the Naples Museum (Lucas, p. 287). Perkin and
Everest say (p. 23):
About the time of the Crusades the cultivation of madder was introduced into Italy and probably
also into France. The Moors cultivated it in Spain, and during the sixteenth century it was brought
to Holland. Colbert introduced it into Avignon in 1666, Frantzen into Alsace in 1729, but only
toward 1760-1790 did it become important. During the wars of the Republic, its cultivation was
largely abandoned, and only after 1815 did this again become regular.
Madder lake and rose madder for artists' pigments are prepared from the
madder extract by adding alum and precipitating with an alkali (Colour Index,
p. 296; see also Perkin and Everest, pp. 623-625). Thompson thinks that the
madder lakes were less employed in mediaeval painting than were the brazil
lakes. He says (The Materials of Medieval Painting, pp. 123-124) that pure
madders, as they are known now, came into use in the XVII and XVIII centuries
and that they were not important in the Middle Ages.
Madder was the source of the dye, Turkey red, formerly used in large quan-
tities in textiles and is still the color for French military cloth (Colour Index,
p. 296). The cultivation of the madder root and its employment for dyeing and
pigment purposes almost ceased shortly after a synthetic method for making
alizarin was discovered by the German chemists, Graebe and Lieberman, in 1868
(see Alizarin).
The ^extract from the madder root also contains another natural dye called
'purpurin.* This is closely related chemically to alizarin and is 1,2,4 trihydroxy-
anthraquinone, CuHgOs (Colour Index, p. 251). The presence of purpurin dis-
tinguishes natural alizarin from the synthetic product. Pure purpurin gives lakes