THE BLUE DYES OF CHINA AND INDIA. 123 



INDIAN BLUES. 

 Indigo. — The greater proportion of the indigos of India are prepared 

 from Indigo/era tinctoria, which is extensively cultivated for that purpose. 

 There are two processes for manufacturing indigo ; the one the dry leaf, and 

 the other the green leaf process. The latter is considered the best, and is in 

 most common use. In India the following is the process adopted for the 

 manufacture of green leaf indigo. When the plant begins to flower, it is cut 

 down at about six inches from the ground, and carried to the steeping vats 

 with as little delay as possible, strewn horizontally in the vats and pressed 

 down by means of beams fixed into side posts, bamboos being placed under 

 the beams. Water is immediately run in, just sufficient to cover the plant. 

 If water is not at once let in, the plant will heat, and become spoilt. The 

 time for steeping depends much on the temperature of the atmosphere, and 

 can only be learnt by experience and careful watching of the vats, but in 

 close sultry weather, with the themometer 96° in the shade, eleven or 

 twelve hours are sufficient. In cooler weather, fifteen or sixten hours are 

 requisite. If the plant is very ripe, the vat will be ready earlier than if 

 the plants were young and unripe. The following are indications that the 

 vat is ready to let off: — 



1. As soon as the water begins to fall in the vat. 



2. When the bubbles that rise to the surface burst at once. 



3. On splashing up the surface water it has an orange tinge mingling 

 with the green. 



4. The smell of the water. When ripe, it should have a sweetish, 

 pungent odour, quite different from the raw smell of the unripe green - 

 coloured water. 



About seven men enter the vat and agitate it, either by the hands or 

 with a wooden paddle, at first gently, but gradually increasing as the fecula 

 begins to separate, which is known by the subsidence of the froth, and the 

 change of the colour of the water from green to dark blue. The time 

 necessary for this beating process is generally from If to 3 hours. 



The following tests may be employed to ascertain if the heating has been 

 sufficient. 



1. Take a little of the water in a saucer and let it stand. If the fecula 

 subsides readily, and the water remains of a Madeira colour, the beating- 

 may be stopped. 



2. Dip a coarse cloth in the vat and wring out the water, observing the 

 colour. If green, the beating must be continued, but if a brownish colour, 

 it is ready. 



3. When sufficiently beaten, the surface of the water will, as soon as the 

 beating is suspended, become of a peculiar glassy appearance, and the froth 

 will subside with a sparkle and effervescence like champagne. 



Three or four chatties of cold water or weak lime water are then 

 sprinkled over the surface, to hasten the precipitation of the fecula, which 

 does not completely take place in less than three or four hours. The water 

 is then drawn off from the surface through plug holes in the wall of the 



