114 EXPLOITATION OF PLANTS 
extracted in hot water till the liquor is syrupy, the 
insoluble matter is strained off, and on cooling, the 
pasty mass is cut into cubes and dried. This is known 
as ‘ mangrove cutch.” 
Other brown dyes, once much in favour, walnut, 
alder bark, and sumach from Rhus Coriaria, have now 
practically disappeared from use. 
The third group of mordant dyes, “the alizarine 
group,’’ were formerly the most important of all cotton 
dyes. The two associated colouring matters, alizarin 
and purpurin, are found in the tubers of several plants. 
In Europe the chief source of the dye was Rubia tinctoria, 
which was largely cultivated in Southern France. 
The colour is present in the cortex of the tubers ; these 
were gathered up in their third year, and the plant was 
propagated by shoots. The ground tubers were ex- 
ported and used in alkaline solution for cotton dyeing, 
in neutral solution for wools. 
Madder gives a whole series of brilliant and very fast 
colours with the different mordants. With alum it 
gives the famous turkey red—the fastest known cotton 
dye. This red was used by the ancient Egyptians, and 
in Turkey and Persia madder is still cultivated for 
dyeing hand-made carpets. With chromium madder 
gives a rich red brown, with copper a brown, with tin 
an orange yellow, and with iron dull purples and a 
dingy approach to black. 
When the dye is to be used for cotton printing the 
patterns are stamped upon the material with different 
proportions of the various mordants mixed with tannic 
acid. Afterwards the whole piece is passed through 
the dyeing bath, when the colours are developed upon 
