#Dyeing Wool Blue with Logwood.#--This method of dyeing blue on wool has lost much of its importance since the introduction of the artificial dyes, but it is still employed when a blue fast to milling is wanted. Logwood gives dark navy blue shades. The process is as follows: The wool is first mordanted by boiling for one and a half hours in a bath of 3 lb. bichromate of potash and 2-1/2 lb. of tartar. The operation must be so carried out that the non-oxidising green chrome mordant is developed on the fibre, and therefore the boiling must be thorough. In place of tartar, argols and oxalic acid are frequently used, while lactic acid or lignorosine might be employed. The dyeing is done (p. 152) in a bath of 20 to 25 lb. logwood, or 5 to 8 lb. logwood extract; the bath is started cold, heated slowly to the boil, and kept at that heat for one to one and a half hours. Between the mordanting and dyeing the wool should be well rinsed. DYEING BLUE WITH COAL-TAR DYES. The blue dyes derived from coal tar are very numerous, direct, basic, acid and mordant blues being known. The direct and basic dyes are very little used, but the acid and mordant dyes are extensively employed, as is indicated in the following recipes. #Dyeing with Direct Dyes.# _Pale Blue_.--Prepare a dye-bath with 1/2 lb. Sulphon Cyanine and 10 lb. Glauber's salt. Enter the goods, and work at the boil for one hour, then lift, wash and dry. _Black Blue_.--Prepare a dye-bath with 3 lb. Sulphon Cyanine, 5 lb. Glauber's salt, and 5 lb. acetate of ammonia; work at the boil for one hour. Sulphon cyanine works well with other dye-stuffs, and gives shades which are fast to milling. #Dyeing with Acid Dyes.# _Bright Blue_.--Prepare a bath with 2 lb. borax and 1 lb. Alkali Blue B. Enter the wool at about 170 deg. F., then heat to the boil, and work for half an hour; then lift, rinse lightly, and pass into a weak sour bath, with sulphuric acid to raise to the colour. Soda may be used in place of borax, but the latter salt maintains the softness of the wool fibre better. By using various brands of Alkali Blue (3 R to 7 B), various shades of blue from a reddish with the 3 R to a pure blue with the 6 B and 7 B brands may be dyed. The Alkali Blues are fairly fast to light. _Dark Blue_.--Prepare a dye-bath with 2 lb. Serge Blue, 10 lb. Glauber's salt, and 2 lb. sulphuric acid, working at the boil (p. 153) for one hour. This is a very common way of dyeing blues on serges, cashmeres and worsted goods. In place of serge blue, what are known as Blackley blues, or Dewsbury blues, may be employed. These have a similar composition, but vary a little in the tint of blue they give. _Navy Blue_.--Prepare a dye-bath with 2 lb. Induline A, 10 lb. Glauber's salt, and 2 lb. sulphuric acid, working at the boil for one hour.