Stannate of soda is easily decomposed by acids; even the carbonic acid present in the air will bring about this change. The tin contained in the stannate is deposited on the cotton in the form of stannic oxide, or, more strictly, stannic acid. As this is somewhat soluble in acids, it is important that the sulphuric acid bath be not too strong, or there will be a tendency for the tin oxide to be dissolved off the cotton, and then but weak shades will be obtained in the final operation of dyeing.
Further, owing to the decomposition of the stannate by exposure to the air, it is important that the substance should be used while fresh, and that only fresh baths should be used.
=(3) Dyeing with Eosine Colours.=--After the treatment with stannate of soda and sulphuric acid the prepared cotton is ready for dyeing. This process is carried out by preparing a cold bath with the required dye-stuff, entering the cotton therein, and then slowly raising to about 180 F., and maintaining at that heat until the desired shade is obtained. It is not needful to raise to the boil and work at that heat.
No better results are obtained, while there is even a tendency for colours to be produced that rub badly, which is due to the too rapid formation of the colour lake; and it is worthy of note that when a colour lake is rapidly formed on the fibre in dyeing it is apt to be but loosely fixed, and the colour is then loose to both washing and rubbing.
_Dyeing with Acid and Azo Dyes._
In dyeing with this class of colours stannate of soda, acetate of lead or alum may be used as mordants. The stannate of soda is employed in the same manner as when the eosines are used, and, therefore, does not require to be further dealt with.
Acetate of lead is used in a similar way. The cotton is first steeped in a bath of acetate of lead of about 10 Tw. strong, used cold, and from half an hour to an hour is allowed for the cotton to be thoroughly impregnated with the lead solution, it is then wrung and passed a second time into a bath of soda, when lead oxide or lead carbonate is deposited on the cotton. After this treatment the cotton is ready for dyeing with any kind of acid, azo and even eosine dyes, and this is done in the same manner as is used in dyeing the eosines on a stannate mordant. The shades obtained on a lead mordant cannot be considered as fast; they bleed on washing and rub off badly.
When alum is used as the mordant it may be employed in the same way as acetate of lead, but as a rule it is added to the dye-bath direct, and the dyeing is done at the boil. This latter method gives equally good results, and is more simple.
The eosines and erythrosines, water blues, soluble blues, croceine scarlets, cloth scarlets, and a few other dyes of the azo and acid series are used according to this method. The results are by no means first class, deep shades cannot be obtained, and they are not fast to washing, soaping and rubbing.
The methods of employing the much more important group of colouring matters known as the mordant dyes, which comprise such well-known products as logwood, fustic and alizarine, require more attention. With these, alumina, iron, and chromium mordants are used as chief mordants, either alone or in combination with one another, and with other bodies.
The principal point is to obtain a good deposit of the mordant on the cotton fibre, and this is by no means easy.
There are several methods by the use of which a deposit is formed of the mordant, either in the form of metallic oxide (or, perhaps, hydroxide) or of a basic salt. In some cases the cotton is passed through alternate baths containing, on one hand, the mordanting salt, _e.g._, alum, copperas, etc., and, on the other, a fixing agent, such as soda or phosphate of soda. Or a mordanting salt may be used, containing some volatile acid that on being subjected to a subsequent steaming is decomposed. Both these methods will be briefly discussed.
_Methods of Mordanting._
The cotton is first steeped in a bath containing Turkey-red oil, and is then dried. By this means there is formed on the fibre a deposit of fatty acid, which is of great value in the subsequent dyeing operations to produce bright and fast shades. After the oiling comes a bath of alum or alumina sulphate, either used as bought, or made basic by the addition of soda. The result is to bring about on the fibre a combination of the fatty acid with the alumina. Following on the alum bath comes a bath containing soda or phosphate of soda, which brings about a better fixation of the alumina.
These operations may be repeated several times, especially when a full shade having a good degree of fastness is desired, as, for instance, Turkey-reds from Alizarine. This method of mordanting is subject to considerable variations as regards the order in which the various operations are carried out, the strength of the baths, and their composition. A great deal depends upon the ultimate result desired to be obtained, and the price to be paid for the work.
Iron is much easier to fix on cotton than is either alumina or chrome.
It is usually sufficient to pass the cotton through a bath of either copperas or iron liquor, hang up to dry or age, and then pass into a bath of lime, soda or even phosphate of soda. The other mordants require two passages to ensure proper deposition of the mordant on the fibre.
Following on the mordanting operations comes the dyeing, which is carried out in the following manner. The bath is made cold with the required amount of dye-stuff and not too small a quantity of water, the cotton is immersed and worked for a short time to ensure impregnation, then the temperature is slowly raised to the boil. This operation should be carefully carried out, inasmuch as time is an important element in the dyeing with mordant colours; the colouring principle contained in the dye-stuff must enter into a chemical combination with the mordant that has been fixed on the fibre. Heat greatly assists this being brought about, but if the operation is carried on too quickly, then there is a tendency for uneven shades to be formed. This can only be remedied by keeping the temperature low until the dye-stuff has been fairly well united with the mordant, and then maintaining the heat at the boil to ensure complete formation of the colouring lake on the fibre, and therefore the production of fast colours.
It has been noticed in the dyeing of alizarines on both cotton and wool that when, owing to a variety of circumstances, local overheating of the bath happens to take place dark strains or streaks are sure to be formed. To avoid these care should be taken that no such local heating can occur.
It only remains to add that it is possible to dye a great range of shades by this method, reds with alizarine and alumina; blacks with logwood and iron; greens from logwood, fustic, or Persian berries, with chrome and iron; blues from alizarine blues; greens from Coeruleine or Dinitrosoresorcine, etc.
Another method of mordanting cotton for the mordant group of dye-stuffs is that in which the cotton is impregnated with a salt of the mordant oxide derived from a volatile acid such as acetic acid, and then subjected to heat or steaming. This method is largely taken advantage of by calico printers for grounds, and dyers might make use of it to a much larger extent than they do.
There are used in this process the acetates of iron, chromium and aluminium, and bisulphites of the same metals and a few other compounds.
Baths of these are prepared, and the cotton is impregnated by steeping in the usual way; then it is gently wrung out and aged, that is, hung up in a warm room overnight. During this time the mordant penetrates more thoroughly into the substance of the fabric, while the acid, being more or less volatile, passes off--probably not entirely, but at any rate some of the metal is left in the condition of oxide and the bulk of it as a basic salt. Instead of ageing the cotton may be subjected to a process of steaming with the same results. After this the cotton is ready for dyeing, which is done by the method described in the last section.
There is still another method to be noticed here, that is, one in which a bath is prepared containing both the mordant and the dye-stuff. In this case the character of the mordant must be such that, under the conditions that prevail, it will not form a colour lake with the dye-stuff. Such substances are the bisulphites, if used with the bisulphite compounds of the dye-stuffs; the acetates, if mixed with some acetic acid, may also be used. The process consists in preparing the dye-bath containing both the mordant and the dye-stuff, entering the cotton, steeping for some time, then wringing and steaming. During the latter operation the acid combined with the mordant, being volatile, passes away, and the colouring matter and mordant enter into combination to form the colour lake, which is firmly fixed upon the fibre. Very good results may be obtained by this method.
Lastly, in connection with the mordant colours, attention may be directed to the process of using some of them, which consists in making a solution of the dye-stuff in ammonia, impregnating the cotton with this alkaline solution, and subjecting it to a steaming operation, during which the alkali, being volatile, passes away, leaving the colouring matter behind in an insoluble form. The cotton is next passed into a weak bath of the mordant (preferably the acetates of iron, etc.)., this being used first cold and then gradually heated up. The dye on the fibre and the mordant combine to form the desired colour, which is fixed on the fibre.
The chrome mordants are those which are most commonly applied by the methods here sketched out, and with the large and increasing number of mordant dyes available, the processes should be worth attention from the cotton dyer.
The following recipes give fuller details than the outline sketches of the methods given above for the use of the various dyes produced with the mordant dyes and metallic mordants. In some cases as will be seen other dyes may be added to produce special shades:--
_Dark Olive._--Prepare a bath from 8 lb. cutch, 4 lb. logwood extract, 7 lb. fustic extract, 2 lb. copper sulphate. Work in this for one to one and a half hours at the boil. This bath may be kept standing, adding new ingredients from time to time, and works best when it gets old. Then pass into a cold bath of 3 lb. copperas for one hour, then wash and enter into a new bath of 10 lb. salt, 6 oz. Titan blue 3 B, 6 oz. Titan brown R, 6 oz. Titan yellow Y, work for one hour at the boil, then lift, wash and dry.
_Brown._--Prepare a bath with 20 lb. cutch, 2 lb. copper sulphate, 4 lb.
quercitron extract. Work for one and a quarter hours at the boil, then allow to lie for a day, when the goods are passed into a bath containing 3 lb. bichromate of potash and 1 lb. alum. Work at 150 to 160 F. in this for a few minutes, then allow to lie for four to five hours, wash well and dry.
_Olive._--Work for twenty minutes at 80 F. in a bath of 10 lb. fustic extract, 5 lb. quercitron extract, 2 lb. logwood extract; heat to boil, work for half an hour, then enter in a cold bath of 2 lb. sodium bichromate and 5 lb. copper sulphate; work for twenty minutes, then heat to boil; work for twenty minutes more, wash and dry.
_Pale Brown._--Treat in a hot bath of 25 lb. cutch, 1-3/4 lb. bluestone; work for half an hour in this bath, then lift, wring, and work in a bath of 1-3/4 lb. bichromate of potash for twenty to thirty minutes. Dye in a bath of 2-1/4 lb. alum, 7 oz. Chrysoidin, 14 oz. Ponceau B.
_Fast Brown._--The cotton is heated in a boiling bath containing 20 lb.
cutch, 4 oz. copper sulphate for one hour, it is then treated in a bath containing 8 oz. bichromate of potash for half an hour, then dyed in a bath containing 2 oz. Benzo black blue, 6 oz. Benzo brown N B, 2 lb.
soap, 8 lb. salt, for one hour at the boil, washed and dried.
_Drab._--Dissolve 1/2 lb. cutch, 7 lb. bluestone, 8 lb. extract of fustic; enter goods at 120 F., give six turns, lift and drain. Prepare a fresh bath containing 2 lb. copperas; enter goods, give three turns, lift, and enter fresh bath at 120, containing 2 lb. bichromate of potash, give four turns, drain, wash and dry.
_Coffee Brown._--For one piece, wet out in hot water, run for half an hour upon a jigger in a bath of 6 lb. good cutch, take up and drain in a bath of 8 lb. black iron liquor; drain, run again through each bath and rinse well. Prepare a fresh bath with Bismarck brown, enter at 100 F., heat slowly to 200 F., drain, rinse and dry.
_Dark Brown Olive._--Prepare the dye-bath with 12 lb. cutch, 2 lb.
bluestone, 2-1/2 lb. alum, 10 lb. quercitron extract, 2 lb. indigo carmine 4 lb. turmeric, 1/4 lb. Bismarck brown; boil for one and a half hours, then lift and add 1 lb. copperas; re-enter the goods, give another half-hour, boil, then add 1-1/2 lb. bichromate of potash, work two hours more, then wash and dry.
_Red Drab._--Boil up 10 lb. cutch and 5 lb. sumac; enter the cotton at 140 F., work fifteen minutes and lift. Prepare a fresh bath of 4 lb.
black iron liquor; enter the cotton cold, work ten minutes and lift.
Prepare another bath with 3 lb. bichromate of potash; enter cotton at 160 F., work fifteen minutes, lift and wash. Finish in a fresh bath containing 3 lb. logwood, 6 lb. red liquor; enter cotton at 100 F., work ten minutes, lift, wash and dry.
_Fawn._--Boil up 5 lb. cutch and 5 oz. bluestone, cool to 100 F.; enter, give six turns, lift, and add 2 lb. copperas; re-enter cotton, give four turns, lift and wring. Prepare a fresh bath with 1 lb.
bichromate of potash; enter cotton at 110 F., give five turns, lift, wash and dry.
_Grey Slate._--Boil up 10 lb. sumac, 3 lb. fustic extract; cool down to 120 F., give eight turns, lift and wring. Prepare a fresh bath with 5 lb. copperas; enter cotton cold, give five turns, lift and wash.
_Dark Plum._--Lay down overnight in 30 lb. sumac. Next morning wring and enter in a fresh bath of oxy-muriate of tin 20 Tw., give four turns, lift and wash well in two waters. Boil out 40 lb. ground logwood, 10 lb.
ground fustic, cool bath down to 140 F.; enter cotton, give eight turns, lift and add 1-1/2 gallons red liquor; re-enter yarn, give four turns, lift, wash and dry.
_Pale Chamois._--Work the cotton seven turns in a cold bath of 3 lb.
copperas, then wring and pass into a cold bath of 3 lb. soda ash; work well, wash and dry.
_Dark Brown Olive._--Prepare a bath of 28 lb. fustic, 3/4 lb. logwood, 18 lb. cutch, 4 lb. turmeric, 2 lb. copper sulphate, 3/4 lb. alum; work for an hour at the boil, then sadden in a new bath of 1 lb. bichromate of potash for half an hour, then sadden in a new bath of 1/4 lb. nitrate of iron, working in the cold for half an hour, lift, wash and dry.
_Havana Brown._--Prepare a bath with 4 lb. cutch and 1 lb. bluestone; work at the boil for one hour, then pass through a warm bath of 1/2 lb.
bichromate of potash, 1 lb. sulphuric acid. Wash and dye in a bath of 3/4 lb. Bismarck brown and 4 lb. alum; work for one hour at about 180 F., wash and dry.
_Black._--Prepare a dye-bath with 20 lb. extract of logwood, 4 lb.
cutch, 5 lb. soda ash, 5 lb. copper sulphate. Heat to the boil, enter the cotton, and work well for three hours, then lift, and allow to lie overnight in a wet condition, wash and pass into a bath of 1 lb.
bichromate of potash for half an hour; lift, wash and dry. The dye-bath is not exhausted, and only about one-third of the various drugs need be added for further batches of cotton.
_Reseda Green._--Prepare a bath with 15 lb. cutch, 8 lb. turmeric; work in this for fifteen minutes at about 150 F., then pass through a hot bath of 2 lb. bichromate of potash for one hour, then re-enter into a cutch bath to which has been added, 1 lb. sulphate of iron; work for one hour, then add 2 lb. alum and work half an hour longer, rinse, wash and dry.
_Fawn Brown._--Prepare a dye-bath with 4 lb. cutch, 2 lb. fustic extract; work for one hour at hand heat, then lift, and pass through a bath of 1-1/4 lb. bichromate of potash; work for a quarter of an hour, rinse and pass into a fresh bath of 1 oz. Bismarck brown for ten minutes, then lift, wash and dry.