INDIGO 911 



does contain a little blue-colouring matter, is preferred to woad by many of the French 

 dyers. The materials employed in the ordinary woad or pastel vat, in addition to 

 woad and indigo, are madder, bran, and lime. In the so-called Indian or potash vat, 

 madder, bran, and carbonate of potash are used : in the German vat, bran, carbonate 

 of soda, and quicklime without woad. The chemical action which takes place in the 

 woad vat is not difficult to understand. The nitrogenous matters of the woad begin, 

 when the temperature is raised, to enter into a state of fermentation, which is kept 

 up by means of the sugar, starch, extractive matter, &c., of the madder and bran. In 

 consequence of the fermentation, the indigo-blue becomes reduced, and is then dis- 

 solved by the lime, thus rendering the liquid fit for dyeing. Great care is necessary 

 in order to prevent the process of fermentation from passing into one of putrefaction, 

 which if allowed to proceed would lead to the entire destruction of the indigo-blue in the 

 liquor. If any tendency to do so is observed, it is arrested by the addition of lime, which 

 combines with the acetic, lactic, and other organic acids that commence to form when 

 putrefaction sets in. On the other hand, an excess of lime must also be avoided, since the 

 reduced indigo-blue is thereby rendered insoluble, and unfit to combine with the material. 



The following account of the method of dyeing woollen goods with indigo, as carried 

 on at present in Yorkshire, may suffice to give a general idea of the process : 



The dye-vats employed are circular, having a diameter of 6 feet 6 inches, and a 

 depth of 7 feet, and are made of cast iron fths of an inch in thickness. They are sur- 

 rounded by brickwork, a space of 3 inches in width being left between the brickwork 

 and the iron, for the purpose of admitting steam, by means of which the vats are 

 heated. The interior surface of the brickwork is well cemented. In setting a vat 

 the following materials are used : 5 cwts. of woad, 30 Ibs. of indigo, 56 Ibs. of bran, 

 7 Ibs. of madder, and 10 quarts of lime. The woad supplied to the Yorkshire dyers 

 is prepared and grown in Lincolnshire. It is in the form of a thick brownish-yellow 

 paste, having a strong ammoniacal smell. The indigo is ground with water in the 

 usual manner. The madder acts in promoting fermentation, but it also serves to give 

 a reddish tinge to the colour. The lime is prepared by putting quicklime into a 

 basket, then dipping it in water for an instant, lifting it out again, and then* passing 

 it through a sieve, by which means it is reduced to a fine powder, called by the dyers 

 ware. The vat is first filled with water, which is heated to 140 Fahr., after which 

 the materials are put in, and the whole is well stirred until the woad is dissolved or 

 diffused, and it is then left to stand undisturbed over night. At 6 o'clock the next 

 morning the liquor is again stirred up, and 5 quarts more lime are added. At 10 

 o'clock, 5 pints of lime are again thrown in, and at 12 o'clock the heat is raised to 

 120 Fahr., which temperature must be kept up until 3 o'clock, when another quart 

 of lime is introduced. The vat is now ready for dyeing. When the process of fer- 

 mentation is proceeding in a regular manner, the liquid, though muddy from insoluble 

 vegetable matter in suspension, is of a yellow or olive-yellow colour ; its surface is 

 covered with a blue froth or a copper-coloured pellicle, and it exhales a peculiar 

 ammoniacal odour ; at the bottom of the vat there is a mass of undissolved matter, of 

 a dirty yellow colour. If there is an excess of lime present, the liquor has a dark 

 green colour, and is covered with a greyish film, and when agitated, the bubbles which 

 are formed agglomerate on the surface, and are not easily broken. Cloth dyed in a 

 liquor of this kind loses its colour on being washed. This state of the vat is remedied 

 by the addition of bran, and is of no serious consequence. When, on the other hand, 

 there is a deficiency of lime, or in other words, when the fermentation is too active, 

 the liquor acquires first a drab, then a clay-like colour ; when agitated, the bubbles 

 which form on its surface burst easily, and when stirred up from the bottom with a 

 rake it effervesces slightly, or frets as the dyers say. If the fermentation be not 

 checked at this stage, putrefaction soon sets in, the liquid begins to exhale a fetid 

 odour, and when stirred evolves large quantities of gas, which burn with a blue flame 

 on the application of a light. The indigo is now totally destroyed, and the contents 

 of the vat may be thrown away. No further addition of woad is required after the 

 introduction of the quality taken in first setting the vat, the fermentation being kept 

 up by adding daily about 4 Ibs. of bran, together with 1 quarter 3 pints of lime. In- 

 digo is also added daily, for about 3 or 4 months. The vat is then used for the purpose 

 of dyeing light shades, until the indigo contained in it is quite exhausted, and its 

 contents are then thrown away. 



Woollen cloth before being dyed is boiled in water for 1 hour, then passed im- 

 mediately into cold water. If it be suffered to lie in heaps immediately after being 

 boiled, ^it undergoes some change, which renders it afterwards incapable of taking up 

 colour in the vat. When a purple bloom is required on the cloth, it is dyed with cud- 

 bear to a light purple shade before being dipped. In dyeing, the cloth is placed on a 

 network of rope attached to an iron ring, which is suspended by four iron chains at 

 a depth of about 3 feet beneath the surface of the liquor. The cloth is stirred about 



