$2	painting materials
Toluidine Red (toluidine toner) is a synthetic, yeltowish red, organic dyestuff,
-nitro-^-toluene-azo-0-naphthol, dvHisNsOs (Colour Index, p. 16). It is one of
he most permanent of its kind and, hence, is now used widely for outside pur-
>oses where a permanent, bright red paint is demanded; it will stand strong
unlight for some months without fading. It is unaltered by heat up to 150° C.
.nd by alkalis, is insoluble in water but soluble in boiling alcohol. Toluidine red
<ras first made by the Badische Company in Germany, the patents being dated
905. Although it has not been offered to the artists' trade under this name, it
lay occasionally be found in cheaper artists' colors as a toner or as a substitute.
Toner is a term used in the heavy paint industry to indicate pure or nearly
»ure synthetic, organic dyestuffs or lakes of high color concentration. Toners are
ometimes used to bring color mixtures of pigments up to standards of tint (see
Iso Para Red, Toluidine Red, etc.).
Transparent White (see Aluminum Hydrate).
Turnsole, a blue from seeds of the plant, Crozophora tinctoria, indigenous to
outhern Europe, is an indicator dye like litmus. When freshly squeezed from the
eeds, it is red; but when made alkaline, it turns blue. In mediaeval times, small
.nen cloths were dyed directly with the juice of the seeds and, when dipped in a
urn solution, served as a convenient source of the color for manuscript painting,
f violet was desired, the cloths were first limed to neutralize the acidity of the
sed juice. Turnsole violet was highly esteemed in XIV century Italy (Thompson,
^rhe Materials of Medieval Painting, pp. 143-144), and was used occasionally to
one azurite.
Tuscan Red is a red iron oxide brightened with one of the more permanent
rganic pigments like alizarin red.
Tyrian Purple, one of the most important and most costly of the organic color-
ng matters of the ancients, was prepared from several mollusks (whelks) including
Vturex brandaris and Purpura haemostoma, found on the shores of the Mediter-
anean and the Atlantic coast, including the British Isles. Huge quantities of these
nollusks were used for dyeing fabrics in classical times, and on certain shores of
he Mediterranean there still remain heaps of the shells about the sites of ancient
lye works. The color-producing secretion of the whelk is contained in a little vein
>r cyst, and when this is broken and squeezed by hand, it issues as a white fluid.
Cloths to be dyed are dipped in this fluid and are exposed to strong sunlight
which causes the development of the color finally to purplish red or crimson. The
lue obtained depends somewhat on the particular species of mollusk and on the
extraction process. P. Friedlander, in his experiments on the extraction of purple
^:rom Murex brandaris collected at Trieste in 1908, obtained only 1.4 grams of the
pure dye from 12,000 mollusks. It was he who established the identity of the
coloring principle as 6:6' dibromoindigotin (' Uber den Farbstoff des antiken
Purpurs aus murex brandaris,' Berichte der Deutschen Chemischen Geselkchaft,
XLII [1909], pp. 765-770). The purple color is remarkably stable, resisting alka-