_Dyeing_--For dyeing, water free from lime must be used. Water having not more than 2.5 hardness can be employed if it is corrected with acetic acid, thereby converting the carbonate of lime into acetate of lime. Very calcareous water must be freed from lime before use. The dye-bath contains for 100 lb. cotton 15 lb. Alizarine blue paste (A R or F, according to the shade desired), 35 lb. acetic acid (12 Tw.), 15-1/2 lb. ammonia (25 per cent.), 2-1/4 oz. tannin. The cotton is worked a quarter of an hour in the cold; the temperature is raised slowly to a boil, taking about one hour, and the cotton is worked three-quarters of an hour at that heat. Finally the cotton is washed and hydro-extracted.
The dyed and washed cotton is steamed two hours at 15 lb. to 22 lb.
pressure. Steaming turns the shade greener and darker, and increases the fastness. After steaming the cotton it is soaped one or two hours at the boil, with or without pressure. According to the quality of water employed, 2 to 5 parts soap per 1,000 parts water are taken.
_Brown._--A fine brown is got by a similar process to this, if instead of Alizarine blue, Alizarine orange is used in the dye-bath. A deeper brown still if Anthracene brown, or a mixture of Anthracene brown and Alizarine blue, be used.
_Claret Red._--Clarets to maroon shade of red are got by preparing the cotton as for blue given above, then dyeing with alizarine.
_Logwood Black._--One of the most important colours that come under this section is logwood black, the formation of which on the fibre depends upon the fact that the colouring principle of logwood forms a black colour lake with iron and also one with chromium.
There are many ways of dyeing logwood blacks on cotton, whether that be in form of hanks of yarns, warps or pieces. While these blacks may be, and in the case of hanks are, dyed by what may be termed an intermittent process, yet for warps and piece goods a continuous process is preferred by dyers. Examples of both methods will be given. As in the dyeing of Turkey reds it is probable that no two dyers of logwood blacks quite agree in the details of their process, there may be variations in the order of the various baths and in their relative strengths. Typical methods will be noted here.
=Dyeing Logwood Black on Yarn in Hanks.=--Operation 1. Sumacing: Prepare a bath with 10 lb. sumac extract in hot water. Work the yarn in this for half an hour, then allow to steep for six hours or overnight, lift and wring. The liquor which is left may be used again for another lot of yarn by adding 5 lb. sumac extract for each successive lot of yarn. In place of using sumac the cheaper myrabolam extract may be used.
Operation 2. Ironing or Saddening: Prepare a bath with 3-1/2 gallons nitrate of iron, 80 Tw. Work the yarn in this for fifteen minutes, then wring out. The bath may be used again when 1 gallon of nitrate of iron is added for each lot of yarn worked in it. In place of the nitrate of iron, the pyrolignite of iron or iron liquor may be used.
Operation 3. Liming: Work for ten minutes in a weak bath of milk of lime.
Operation 4. Dyeing: This is done in a bath made from 10 lb. logwood extract and 1 lb. fustic extract. The yarn is entered into the cold or tepid bath, the heat slowly raised to about 150 F, then kept at this heat until a good black is got, when the yarn is taken out, rinsed and wrung. The addition of the fustic extract enables a much deeper and jetter shade of black to be dyed.
Operation 5. Saddening: To obtain a fuller black the dyed cotton is sent through a bath of 1-1/2 lb. of copperas, then washed well.
Operation 6. Soaping: Work for twenty minutes in a bath of 2 lb. soap at 140 to 150 F. Then wash well.
Much the same process may be followed for dyeing logwood black on warps and piece goods, jiggers being used for each operation.
Another method is to first work the cotton in pyrolignite (iron liquor) at 10 Tw., until it is thoroughly impregnated, then to dry and hang in the air for some hours, next to pass through lime water to fix the iron, and then to dye as before.
_Continuous Process._--In this case a continuous dyeing machine is provided, fitted with five to six compartments. The cotton is first of all prepared by steeping in a bath of 12 lb. myrabolam extract for several hours, then it is taken to the continuous machine and run in succession through nitrate of iron liquor, lime water, logwood and fustic, iron liquor and water. The nitrate of iron bath contains 2 gallons of the nitrate to 10 gallons of water, and as the pieces go through fresh additions of this liquor are made from time to time to keep up the volume and strength of the liquor to the original points.
The logwood bath is made from 10 lb. logwood extract and 1 lb. fustic extract, and it is used at about 160 F. The quantities here given will serve for 100 lb. of cotton, and it is well to add them dissolved up in hot water in small quantities from time to time as the cotton goes through the bath.
The iron liquor given after the dyeing contains 2 lb. of copperas in 10 gallons of water.
Between the various compartments of the machine is fitted squeezing rollers to press out any surplus liquor, which is run back into the compartment. The rate of running the warp or pieces through should not be too rapid, and the dyer must adapt the rate to the speed with which the cloth dyes up in the dye-bath.
The addition of a little red liquor (alumina acetate) to the iron bath is sometimes made, this is advantageous, as it results in the production of a finer black. Iron by itself tends to give a rusty-looking, or brownish black, but the violet, or lilac shade that alumina gives with logwood, tones the black and makes it look more pleasant.
Some dyers add a small quantity, 1 per cent., of the weight of the cotton of sulphate of copper to the iron bath, others add even more than this. Some use nitrate of copper; the copper giving a greenish shade of black with logwood, and this tones down the iron black and makes it more bloomy in appearance.
Single bath methods of dyeing logwood blacks are in use, such methods are not economical as a large quantity, both of dye-wood and mordants, remain in the bath unused. Although full intense blacks can be dyed with them, the black is rather loosely fixed and tends to rub off. This is because as both the dye-stuff and the mordant are in the same bath together they tend to enter into combination and form a colour lake that precipitates out in the dye-bath, causing the loss of material alluded to above, while some of it gets mechanically fixed on the cotton, in a more or less loose form, and this looseness causes the colour to rub off.
For a _chrome-logwood black_, a dye-bath is made with 3 lb. bichromate of potash, 100 gallons logwood decoction at 3 Tw., and 6-1/2 lb.
hydrochloric acid. Enter the cotton into the cold bath, raise slowly to the boil and work until the cotton has acquired a full black blue colour, then take it out and rinse in a hot lime water when a blue black will be got.
A _copper-logwood black_ is got by taking 100 gallons logwood decoction at 3 Tw., and 6 lb. copper acetate (verdigris); the cotton is entered cold and brought up to the boil. Copper nitrate may be used in the place of the copper acetate, when it is a good plan to add a little soda to the bath. Some dyers in working a copper-logwood black make the dye-bath from 100 gallons logwood liquor at 2 Tw., 4 lb. copper sulphate (bluestone) and 4 lb. soda. This bath is used at about 180 to 190 F., for three-quarters of an hour, then the cotton is lifted out, wrung and aged or as it is sometimes called "smothered" for five hours. The operations are repeated two or three times to develop a full black.
Logwood black dyeing has lost much of its importance of late years owing to the introduction of the many direct blacks, which are much easier of application and leave the cotton with a fuller and softer feel.
_Logwood Greys._--These are much dyed on cotton and are nothing more than weak logwood blacks, and may be dyed by the same processes only using baths of about one-tenth the strength.
By a one-bath process 5 lb. of logwood are made into a decoction and to this 1 lb. of copperas (ferrous sulphate) is added and the cotton is dyed at about 150 F. in this bath. By adding to the dye-bath small quantities of other dye-woods, fustic, peach wood, sumach, etc., greys of various shades are obtained. Some recipes bearing on this point are given in this section.
Logwood is not only used for dyeing blacks and greys as the principal colouring matter, but is also used as a shading colour along with cutch, fustic, quercitron, etc., in dyeing olives, browns, etc., and among the recipes given in this section examples of its use in this direction will be found.
The dye-woods--fustic, Brazil wood, bar wood, Lima wood, cam wood, cutch, peach wood, quercitron bark, Persian berries--have since the introduction of the direct dyes lost much of their importance and are now little used. Cutch is used in the dyeing of browns and several recipes have already been given. Their production consists essentially in treating the cotton in a bath of cutch, either alone or for the purpose of shading with other dye-woods when the cotton takes up the tannin and colouring matter of the cutch, etc. The colour is then developed by treatment with bichromate of potash, either with or without the addition of an iron salt to darken the shade of brown.
The usual methods of applying all the other dye-woods, to obtain scarlets to reds with Brazil wood, Lima wood, peach wood; or yellows with fustic, quercitron or Persian berries, is to first prepare the cotton with sumac, then mordant with alumina acetate or tin crystals (the latter gives the brightest shades), then dye in a decoction of the dye-woods. Sometimes the cotton is boiled in a bath of the wood when it takes up some of the dye-wood, next there is added alumina acetate or tin crystals and the dyeing is continued when the colour becomes developed and fixed upon the cotton.
Iron may be used as a mordant for any of these dye-woods but it gives dull sad shades.
Chrome mordants can also be used and these produce darker shades than tin or alumina mordants.
As practically all these dye-woods are now not used by themselves it has not been deemed necessary to give specific recipes for their application, on previous pages several are given showing their use in combination with other dyes.
The dye-stuff Dinitroso-resorcine or Solid green O is used along with iron mordants for producing fast greens and with chrome mordants for producing browns to a limited extent in cotton dyeing. The following recipes give the details of the process.
_Green._--Steep the cotton yarn or cloth in the following liquor until well impregnated, then dry: 3 gallons iron liquor (pyrolignite of iron), 22 Tw. gallons of water, 3/4 gallon acetic acid, 12 Tw., 2 lb.
ammonium chloride. Then pass the cotton through a warm bath of 3 oz.
phosphate of soda and 4 oz. chalk per gallon, then enter into a dye-bath containing 6 lb. Solid green O. Work as described for dyeing alizarine red. For darker greens of a Russian green shade use 10 lb. of solid green O, in the dye-bath.
_Brown._--A fine brown is got by steeping the cotton in a bath of 8 lb.
Solid green O, 6-3/4 gallons water, 1-1/2 gallons ammonia and 2 lb.
acetate of chrome; dry, then pass through a soap-bath, wash and dry.
_Deep Olive Brown._--Mix 8 lb. Solid green O and 4-1/2 lb. borax with 6 gallons water, add 1/2 lb. Turkey-red oil, 5 lb. ammonia, then 2 gallons water and 1-1/2 lb. copper-soda solution and another 2 gallons water.
Steep the cotton in this, dry, soap well and wash. The copper-soda solution is made from 10 lb. chloride of copper (75 Tw.), 5 lb.
tartaric acid, 12 lb. caustic soda (75 Tw.) and 4 lb. glycerine.
_Khaki._--Make the dye liquor from 14 lb. Solid green O, 1/2 lb.
Alizarine yellow N, 1 lb. caustic soda (36 Tw.), 1/2 lb. Turkey-red oil and 8 gallons water. To this add 2-1/2 lb. acetate of chrome (32 Tw.), 2-1/4 lb. copper-soda solution and 4 gallons water.
_Sage Green._--Use 1-1/4 lb. Solid green O, 3 lb. caustic soda (36 Tw.), 1/2 lb. Ceruleine, 1/2 lb. Turkey-red oil, 1 gallon water to which is added 2-1/2 lb. acetate of chrome (32 Tw.) and 2-1/4 lb. copper-soda solution dissolved in 4 gallons water.
_Pale Brown._--Use 4 lb. Solid green O, 2-1/2 lb. borax, 3 lb. ammonia, 1/2 lb. Turkey-red oil, 6 gallons of water and 1-1/2 lb. copper-soda solution dissolved in 2 gallons water.
_Pale Fawn Brown._--The dye-bath is made from 1/2 lb. Alizarine, 1-1/4 lb. Solid green O, 1-1/2 lb. borax, 1/2 lb. Turkey-red oil and 5 gallons of water to which is added 1-1/2 lb. acetate of chrome (32 Tw.), 1-1/2 lb. copper-soda solution and 4 gallons water. In all cases the cotton is steeped in the dye liquors until thoroughly impregnated, then the excess liquor is wrung out, the cotton dried, then passed through a soap bath, washed well and dried.
_Dark Brown._--Place the cotton in a lukewarm bath of 25 lb. cutch and 1-1/2 lb. copper sulphate; work for half an hour, then steep for six hours, then lift, wring and enter into a bath of 3-1/4 lb. bichromate of potash at 160 F. for twenty minutes. Then wash and dry.
_Yellow Brown._--Make a bath with 14 lb. cutch and 1/2 lb. copper sulphate; work in this bath for four hours at 120 F., then pass into a bath of 2 lb. copperas and 1/2 lb. chalk, work for half an hour in the cold, then pass into a hot bath of 2-1/2 lb. bichromate of potash at 150 F. for half an hour.
_Dark Brown._--Make a dye-bath with 15 lb. cutch, 2 lb. logwood extract and 2 lb. fustic extract; work the cotton in this at 160 F. for three hours, then pass into a cold bath of 1 lb. copperas and 1/4 lb. chalk for half an hour, then into a bath of 3 lb. bichromate of potash for half an hour at 150 F., then wash and dry.
(7) PRODUCTION OF COLOUR DIRECT UPON COTTON FIBRES.
By the action of nitrous acid upon the salts of the primary organic amines the so-called diazo compounds are formed. An example of this important process is that of nitrous acid on aniline hydrochloride shown in the following equation:--