Part 5 (2/2)

INDIGO, WOAD, LOGWOOD

_INDIGO_

Indigo is the blue ofera tinctoria_ and other species, growing in Asia, South Aypt It reaches the market in a fine powder, which is insoluble in water There are tays of dyeing with Indigo It may be dissolved in sulphuric acid or oil of vitriol, thereby o extract

This process was discovered in 1740 It gives good blue colours but is not very permanent, darker colours are more so than the paler It does not dye cotton or linen

The other o vat process which produces fast colours but is coo it has to be deprived of its oxygen The deoxidized indigo is yellow and in this state penetrates the woollen fibre; the hter and faster will be the colour For wool dyeing the vats are heated to a teenerally dyed cold

TO MAKE EXTRACT OF INDIGO

1 lb oil of vitriol (pure, not coo

1/2 oz precipitated chalk

Mix a little of the indigo with a small quantity of oil of vitriol, add a little chalk and stir well Go on radually till all is used up This should take an hour or two Stir a few ti about 1/2 oz lass stoppered bottle or jar, and stirred with a glass rod It must be kept from the air

INDIGO EXTRACT (4 to 6 lbs wool)

Mordant[E] 25 Aluo extract into the water of dye bath The amount is determined by the depth of shade required

When war 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 butto 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 wood a little madder is sometimes used; also Cudbear or Barwood

INDIGO VAT (TIN) FOR WOOL

To 2 quarts of water add 1/4 lb lio pounded up with a little of the liet warmer Pound up 1/2 oz tin, _Stannous Chloride_, in a little liether with 1/2 oz zinc Addto the state of the vat There should be a streaky scureen 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 12)

4 pints Sodium Hydrosulphite (SG 11)

_The Stock Solution_--Take 2 ozs of well pounded indigo, with enough ater (120F) to rind_ in a pestle and allon Take 12 fluid ozs of water adding gradually 3 ozs of coive a solution of SG 12, which can be tested with a hydro SG 1 as for water

Next take 5 pints water, add hydrosulphite slowly, stirring gently until a reading of 1100 is shown (SG 11) on the hydrohed beforehand and the stock of the sareat heat, for future vats the hydrohed out and added slowly to the water If added too quickly the hydrosulphite will cake, fall to the bottom and be difficult to dissolve

To the saucepan containing the indigo (100 per cent) add 7 fluid ozs

of the caustic soda solution, then gradually add 3-1/2 pints of hydrosulphite solution, stirring gently for 15 to 20 minutes Heat the saucepan to 120F and on no account towill ruin the Stock Solution_--let it stand for half an hour, then test with a strip of glass This should show a perfectly clear golden yellow colour (turning blue in 45 secs approx), free froo, therefore gradually add hydrosulphite solution (2-3 fluid ozs) Wait 15 lass strip; if incorrect continue this every 15 lass indicates clear yellow If the Stock Solution is greenish white and turbid, undissolved _indigo white_ is present Add then not more than a teaspoonful at a time caustic soda solution until the Stock Solution answers the glass test