Mordant[E] 25% Alum. Stir 2 to 3 ozs. Indigo extract into the water of dye bath. The amount is determined by the depth of shade required. When warm, enter the wool and bring slowly to boiling point (about 1/2 an hour) and continue boiling for another 1/2 hour. By keeping it below boiling point while dyeing, better colours are got, but it is apt to be uneven. Boiling levels the colour but makes the shade greener. This is corrected by adding to the dye bath a little logwood, 10 to 20 per cent which should be boiled up separately, strained, and put in bath before the wool is entered; too much logwood dims the colour. Instead of logwood a little madder is sometimes used; also Cudbear or Barwood. INDIGO VAT (TIN) FOR WOOL To 2 quarts of water add 1/4 lb. lime, and make hot. Then add 1 oz. indigo pounded up with a little of the lime water; let it stand and get warmer. Pound up 1/2 oz. tin, _Stannous Chloride_, in a little lime water and add, together with 1/2 oz. zinc. Add more lime water or tin according to the state of the vat. There should be a streaky scum on the surface, and the water underneath clear with a green tinge. Pearl ash can be used instead of lime. HYDROSULPHITE-SODA VAT FOR WOOL 2 ozs. powdered indigo. 7 fluid ozs. Caustic Soda solution (SG 1.2). 4 pints Sodium Hydrosulphite (SG 1.1). _The Stock Solution._--Take 2 ozs. of well pounded indigo, with enough warm water (120 deg.F.) to make a paste, and _grind_ in a pestle and mortar for 10 minutes. Empty into a saucepan, capacity 1 gallon. Take 12 fluid ozs. of water adding gradually 3 ozs. of commercial caustic soda 76 per cent. This will give a solution of SG 1.2, which can be tested with a hydrometer reading from 1000 to 2000, the 1000 representing SG 1 as for water. Next take 5 pints water, add hydrosulphite slowly, stirring gently until a reading of 1100 is shown (SG 1.1) on the hydrometer. If the hydrosulphite be weighed beforehand and the stock of the same be kept free from damp air, or great heat, for future vats the hydrometer can be dispensed with; it is simply weighed out and added slowly to the water. If added too quickly the hydrosulphite will cake, fall to the bottom and be difficult to dissolve.