Although almost all dyeing can be done in a vat, the term vat dye is used to describe a chemical class of dyes that are applied to cellulosic fibre (i.e. cotton) using a redox reaction as described below. Because of the use of caustic soda, and the very high pH of the dye bath in the dyeing process, wool cannot be dyed using vat dyestuffs. Wool is soluble in caustic soda solutions. It is possible to dye wool at room temperatures with indigo (vat blue 1) and other low substantive vat dyes using soda ash as the alkali source with very little strength loss. Vat red 10, vat violet 13 and vat orange 1 can be applied in this manner as well.