Cetraria Islandica. Iceland moss. Iceland heaths, and hills. It yields a good brown to boiling water, but this dye appears only to have been made available to the Icelanders.
Parmelia physoides. Dark crottle, Bjork-laf. Found in Sweden, Scotland & Scandinavia, on rocks and trees.
P. omphalodes. In Scandinavia and Scotland. Withering asserts that it yields a purple dye paler, but more permanent, than orchil; which is prepared in Iceland by steeping in stale lye, adding a little salt and making it up into balls with lime.
Sticta pulmonacea. Oak lung, Lungwort, Aikraw, Hazel-raw, Oak rag, Hazel rag, Hazel crottle, Rags. Found on trees in England, Scotland, North of Ireland, Scandinavia. It dyes wool orange and is said to have been used by the Herefordshire peasantry to dye stockings brown. Some species yield beautiful saffron or gamboge coloured dyes, e.g. S. flava, crocata, aurata.
For continuation of list see [Appendix].
CHAPTER VI.
[12] BLUE
INDIGO, WOAD, LOGWOOD.
"Notwithstanding the very great facility of dyeing wool blue, when the blue vat is once prepared, it is far otherwise with regard to the preparation of this vat, which is actually the most difficult operation in the whole art of dyeing."—Hellot.
INDIGO
Indigo is the blue matter extracted from a plant, Indigofera tinctoria & other species, growing in Asia, South America and Egypt. It reaches the market in a fine powder, which is insoluble in water. There are two ways of dyeing with indigo. It may be dissolved in sulphuric acid or oil of vitriol, thereby making an indigo extract. This process was discovered in 1740. It gives good blue colours, but is not very permanent. Darker colours by this method are more permanent than the paler ones. It does not dye cotton or linen.
The other method is by the indigo vat process, which produces fast colours, but is complicated and difficult. In order to colour with indigo, it has to be deprived of its oxygen. The deoxydised indigo is yellow, and in this state penetrates the woollen fibre; the more perfectly the indigo in a vat is deoxydised, the brighter and faster will be the colour. For the dyeing of wool, the vats are usually heated to a temperature of 50°C. Cotton and linen are generally dyed cold.