Indigo White is fixed on the yarn as Indigo White and on exposure to the air becomes blue. The yarn, on removal from the vat, should come out greenish yellow or a greenish blue. The latter is for blue yarn and should not turn blue too quickly (allow 60 seconds at least). Rest the vats for 1 hour after 3 hours work. Never hurry the vats. It is a good thing to have hydrosulphite slightly in excess as this prevents premature oxidization; too much will strip off the indigo white already deposited on the yarn. Caustic Soda must always be used with the greatest caution or the yarn will be tendered and ruined. Finally, unless the yarn is completely scoured it is impossible to obtain a clear colour, or a blue which will not rub off. The figures given are for Indigo bearing 100% Indigotine, therefore in using vegetable Indigo do not add _all_ the Caustic or Hydrosulphite, but depend on the glass test rather than on measurements. _WOAD_ Woad is derived from a plant, _Isatis tinctoria_, growing in the North of France and in England. It was the only blue dye in the West before Indigo was introduced from India. Since then woad has been little used except as a fermenting agent for the Indigo vat. It dyes woollen cloth a greenish colour which changes to a deep blue in the air. It is said to be inferior in colour to indigo but the colour is much more permanent. The leaves when cut are reduced to a paste, kept in heaps for about fifteen days to ferment, and then are formed into balls which are dried in the sun; these have a rather agreeable smell and are of a violet colour. These balls are subjected to a further fermentation of nine weeks before being used by the dyer. When woad is now used it is always in combination with indigo, to improve the colour. Even by itself, however, it yields a good and very permanent blue. It is not now known how the ancients prepared the blue dye, but it has been stated (Dr. Plowright) that woad leaves when covered with boiling water, weighted down for half-an-hour, the water then poured off treated with caustic potash and subsequently with hydrochloric acid, yield a good indigo blue. If the time of infusion be increased, greens and browns are obtained. It is supposed that woad was "vitrum" the dye with which Caesar said almost all the Britons stained their bodies. It is said to grow near Tewkesbury, also Banbury. It was cultivated till quite lately in Lincolnshire. There were four farms in 1896; one at Parson Drove, near Wisbech, two farms at Holbeach, and one near Boston. Indigo has quite superseded it in commerce. LOGWOOD (_Bois de Campeche, Campeachy Wood_)