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the paste must be mixed with boiling water and kept 

 in a covered vat at a temperature of 110 to 140 Fah. 

 In about 14 hours bubbles of gas begin to rise, forming 

 a froth, when a small quantity of slaked lime is added. 

 This is the finishing touch, this the magic key which opens 

 the enchanted door, for now ! woollen articles which are 

 soaked in the vat and come out olive-green turn blue 

 on exposure to the air. At the same time the scum 

 which accumulates on the surface of the vat turns blue 

 from the same cause, namely oxidation. This blue scum 

 was formerly much in demand for painters, and was the 

 "flowers of woad " which, in 1415, the dyers of Coventry 

 were accused of skimming off the vats in which they 

 dyed their customers' goods, and adding to the vats in 

 which they dyed their own. This same scum, mixed 

 with oil or grease, in all probability formed the pigment 

 which the ancient Britons used in Csesar's time to stain 

 their bodies blue with. Though it is not likely that 

 those people understood the art of dyeing, they must 

 have found out somehow that by infusing Woad leaves 

 and adding an alkali — perhaps wood ashes or a marine 

 plant — a blue scum could be obtained. Now, after all 

 the foregoing, it must come somewhat as a surprise to 

 hear that though Woad was used as a dye per se long 

 before Indigo came into Europe, and still has its uses 

 in dyeing, curiously enough, those uses are not for its 

 blue, whatever colour it may itself be capable of imparting 

 being entirely neglected by the dyer. What, then, is 

 the use of it ? The use of it is to keep up fermentation 

 in vats wherein Indigo is also steeped — " Woad-indigo 

 vats" — whereby that highly insoluble substance is rendered 

 soluble with better and more lasting effect than by any 

 other known means. It is, in short, a fermentative 

 solvent of Indigo. The whole process is a chemically 

 complex one, into which I have neither time nor ability 

 to enter ; but it is an ascertained fact that articles dyed 

 in Woad-indigo vats, though the process is comparatively 



