[1]Many experienced purchasers in this country pay no regard to this mould, as it weighs scarcely any thing.—Ed.
Many experienced purchasers in this country pay no regard to this mould, as it weighs scarcely any thing.—Ed.
Before proceeding to a consideration of the practical applications of indigo in manufacturing, we must pause to make some general observations upon the commerce in indigo.
The first European impulse given to this commerce was made by the Spanish and Portuguese. They not only imported indigo from the Indies, but established its fabrication in their colonies. To them we owe its production in Guatemala, Caraccas, and Brazil. The French exported from the Island of San Domingo, only, in 1774, 2,350,000 pounds weight of this commodity. British influence was exerted in favor of the development of this article in the American colonies, and, in 1773, in the space of twelve months, over a million pounds of indigo were exported from South Carolina. The production in India was at that time of little importance. It was not until 1783 that the attention of the English was directed to the culture of indigo in India for European consumption, that produced by the natives being all consumed in their own manufactures. In the hands of the English this product rapidly rose to be the most important of India, in a commercial view, except that of rice. The small cost of a factory, and the comparatively small capital required forthis production, caused the indigo culture to be preferred to sugar planting. The importation and sale of this commodity at the East India House, in 1792, amounted to 581,827 lbs., while the importation into Great Britain from other parts of the world amounted to 1,285,927 lbs. In 1806 the importation from the East Indies, and sales at the East India House, amounted to 4,811,700 lbs., and produced in sterling money £1,685,275. In the year 1862–63, the export from India, and the destination of supplies, were as follows:—
The value of exports in 1866 was £1,861,501. In the same year the imports of indigo from the whole of Central America, including Honduras, was 672,480 lbs. The consumption of indigo in Great Britain did not increase during the ten years ending with 1867. This stationary demand, notwithstanding the fall in the price of the drug and increase of population, is attributed by McCulloch principally to the decreasing use of blue cloth. It is more probably due to the substitution of cheaper dyes. The average home consumption in Great Britain for seven years ending in 1867, was 1,675,072 lbs. per year.
The importation into this country for the twenty years last past is shown by the following table, kindly prepared at our request by the chief of the Bureau of Statistics:—
Statement of Imports of Indigo into the United States during the Fiscal Years ended June 30, 1853–1872.
EDWARD YOUNG,Chief of Bureau.
Bureau of Statistics, Nov. 16, 1872.
The extraordinary quantity imported in 1862, we hardly need remark, was due to the demand for consumption in army cloths. Indigo imported directly, was made free of duty in 1861. The duty which appears by the above table to have been charged since that period, was upon indigo, the product of India, imported by way of England, which was subject to an extra duty of ten per cent.
The indigo consumed in the United States is generally supplied by the Boston and New York Calcutta houses, who have either an American partner resident in Calcutta, or who employ a resident American as agent. Indigo, like other Calcutta goods,is sold through the agency of brokers, who receive on this article a commission of one per cent. The value of the article is known almost daily in these cities by telegrams, giving exact information of the state of the trade, transmitted from Calcutta as often as every five days. Some of the brokers publish monthly circulars, showing the stock of indigo with other Calcutta goods on hand in our market. The regular trade reports issued by the India merchants show that The higher qualities of indigo do not come to our market. The following is an extract from a report of Whitney, Brother, & Co., of 1871:—
At the present moment there is great depression in the trade in this article. The last telegrams show a decline of price in the Indian trade in this article of from fifty to seventy-five per cent from the prices of last year; and the apprehension is even entertained that indigo is going out of use, the dreaded competitors being the aniline dyes, and particularly the Nicholson blue. We maybe presumptuous in giving our opinion on the question, but we hazard the prediction that, notwithstanding the temporary popularity of the cheap substitutes, a reaction will take place in favor of that “wonderful and most valuable production,” whose importance as a dye has been held in India for thousands of years and Europe for two centuries, “greatly to exceed any other.”[2]
[2]The “Dictionnaire Universel du Commerce,” &c., published in 1861, contains an exhaustive article on the commerce in indigo, by M. S. Beekrode. From the statements of this writer, it appears that the consumption of indigo was estimated, in 1835, as follows:—Great Britain1,214,380kilograms(2,683,779)lbs.France912,915„(2,017,542)„United States130,000„(277,300)„Other countries2,435,473„(5,382,395)„Total4,692,768kilograms(10,362,016)lbs.The approximate consumption in 1859 is stated as follows:—Great Britain800,000kilograms(1,768,000)lbs.France800,000„(1,768,000)„United States400,000„(884,000)„Russia860,000„(1,900,600)„The Zollverein1,250,000„(2,762,500)„Switzerland150,000„(331,500)„Austria400,000„(884,000)„Other countries300,000„(663,000)„Total4,960,000kilograms(10,961,600)lbs.The average production in 1859 is estimated as follows:—Bengal, Madras, &c.3,500,000kilograms(7,735,000)lbs.Java550,000„(1,215,500)„Central America300,000„(884,000)„Other sources100,000„(221,000)„Total4,450,000kilograms(9,834,500)lbs.As the maximum annual consumption in 1859 is set down at 5,000,000 kilograms, the author concludes that the average production at that time did not surpass the requirements of the dyers of the whole world.
The “Dictionnaire Universel du Commerce,” &c., published in 1861, contains an exhaustive article on the commerce in indigo, by M. S. Beekrode. From the statements of this writer, it appears that the consumption of indigo was estimated, in 1835, as follows:—
The approximate consumption in 1859 is stated as follows:—
The average production in 1859 is estimated as follows:—
As the maximum annual consumption in 1859 is set down at 5,000,000 kilograms, the author concludes that the average production at that time did not surpass the requirements of the dyers of the whole world.
As pertinent to the commercial branch of our subject, we must briefly notice the remarkable facts of the sudden growth and equally sudden and extraordinary extinction of the production of indigo in the Carolinas. Indigo was for many years the second great staple of South Carolina. So highly was this staple estimated that the historian of the State declares that “it proved more really beneficial to Carolina than the mines of Mexico or Peru are or ever have been to Old or New Spain.” Its introduction was the happy result of a woman’s culture and energy. In the early part of the last century, the indigo plant had been extensively cultivated in the West India Islands, which then furnished the chief supply of Europe. The governor of Antigua, George Lucas, whose home plantation was at Wappoo in Carolina, having observed the fondness of his daughter, Miss Eliza Lucas, afterwards the mother of General Charles Cotesworth Pinckney, for the culture of plants, was in the habit of sending to her tropical seeds to be sowed on his plantation at Wappoo. Among others, he sent her some seeds of the indigo plant cultivated in the West Indies. She planted them for two years; butthe seeds failed to germinate, or were killed by the frost. On the third year’s trial, in 1741 or 1742, she was successful. Governor Lucas, on hearing that the plants had ripened and produced seed, sent from Montserrat a person skilled in making indigo. Vats were built on Wappoo Creek, and there the first American indigo was manufactured. The attempts of the expert to conceal his processes were defeated by the vigilance of Miss Lucas. The process of manufacture was made known. Seeds from the Wappoo plantation were freely distributed and successfully planted; and the culture of indigo became common. In 1747, a considerable quantity of indigo was sent to England, which induced the merchants trading with Carolina to petition parliament for a bounty on Carolina indigo. In 1748, an act of parliament was passed granting a bounty of sixpence per pound on indigo raised on British-American plantations and imported directly to Britain from its place of growth. This act stimulated the planters of Carolina to double vigor in the production of this new material for export. “Many of them,” says Dr. Ramsay, “doubled their capital every three or four years by planting indigo.” In the year 1754, the export of indigo from the province amounted to 216,924 lbs., and in the years 1772 and 1773 the export had risen to 1,107,661 lbs. The production was greatly checked by the war of the Revolution. Near the close of the century the large importations from India lowered the price, so as to make the planting unprofitable. In the mean time, the culture of cotton had sprung up under the protective tariff of 1789. The grounds suitable for indigo planting were equally fitted for cotton, and were for the most planted with the new staple. It is curious to observe how the former was displaced by the latter staple. The export of indigo from Charleston in 1797 was 96,121 lbs.: in 1800, it fell to 3,400 lbs. During the same years, the exports of cotton rose from one million to six and a half million pounds. The production of American indigo appears to have revived from time to time up to 1829. A writer of that period in Silliman’s Journal of Science estimates—although it would seem on doubtful authority—the production of indigo in the United States at 20,000 lbs. The priceof the American article had fallen, owing to the great quantity of extractive which it contained, to fifty cents per pound, while the Bengal indigo was worth $1.15 per pound. We have no data as to its production at the present time, but infer, from the fact that no reference has been made to this product in the Government Agricultural Reports for many years past, that the production, if any, is too unimportant to be noticed.
All the applications of indigo require that the material should first be reduced to an impalpable powder. It is better to grind it with water, to prevent the loss of material in the form of powder, although the dry pulverization is necessary when the indigo is to be used for the manufacture of the sulphate. To facilitate the grinding the material into a paste, it should be previously soaked in hot water from one to three hours. The grinding on a small scale may be done by a very simple apparatus. This is a hemispherical vessel of copper or cast-iron, eighteen inches in diameter, furnished at the edge with two handles. The workman, sitting astride a bench, places the vessel before him, in which he places three heavy cast-iron balls, the indigo which has been softened, and a sufficient quantity of water. Holding the basin by the handles, he gives it a circular oscillatory movement, in such a manner that the balls, following this movement, crush the indigo which surrounds them; after which the contents are poured into another vessel, water is added, and the material is stirred. The portions incompletely ground are made to reunite themselves at the bottom by means of regular blows with a hammer on the rim of the vessel. The upper liquid is decanted, and the deposit is submitted to a new manipulation in the basin.
In large establishments the grinding is done by machinery. An apparatus highly recommended, consists of two circular plates of cast-iron, arranged horizontally and slightly separated, one from the other, which are rapidly rotated by power, in inverse, directions. The interior surfaces of these disks are provided with deep grooves radiating in a curved line from thecentre to the circumference, and diminishing in depth in the same direction. The indigo which has been previously softened enters between the two plates by an opening in the centre of the upper one, and escapes in a thin paste by the circumference.
The application of indigo to the coloring of textile fabrics requires the complete dissolving of the substance, for which the mechanical division is only a preliminary. There are only two known means of dissolving this substance: 1. By reduction; 2. By the action of concentrated sulphuric acid. The first means allows indigotine to be regenerated; and, when the dyeing is completed, it is pure indigotine which adheres to the colored fibre. By the second means, or dissolving by sulphuric acid, the coloring material enters into a new combination, from which it can never be separated: it becomes a new substance, endowed with new and special properties.
The fixing of Indigotine by means of Reduction.—In this method the operator avails himself of one of the most remarkable qualities of indigotine: this is the facility with which this body takes up hydrogen, and becomes transformed into a colorless substance, which is soluble in favor of alkaline or alkaline-earthy bases, and is susceptible of reproducing indigotine by simple oxidation in contact with air. This hydrogenized substance is called white indigo. Blue indigo, or indigotine, is insoluble except by concentrated sulphuric acid; and this insolubility gives it its superiority to all other blue dyes. Not being soluble, it cannot, as blue indigo, attach itself to the material to be dyed; but in the soluble form of white indigo it can perfectly penetrate the fibre. If by any means of oxidation we can transform the white indigo into blue indigotine, the latter becomes insoluble, and is imprisoned in the pores of the fibre. This is, briefly, the whole theory of the use of indigo in dyeing or printing, although the reaction may be applied in different ways to the coloring of fibres, such as—
1. The indigo is dissolved by means of an alkaline reduction in a vat, and the fibre is immersed in the bath. This is the common blue vat.
2. The solution prepared beforehand is painted by a hairpencil and printed by a stamp or roller upon only certain parts of the tissues. This is the pencil blue.
3. The white indigo is precipitated under the form of a paste, in combination with a metallic oxide having strong reducing power, such as hydrated protoxide of tin, which prevents the too rapid reoxidation of the indigotine. The thickened paste is printed, and the tissue is placed in an alkaline bath (lime or soda), which, displacing the oxide of tin, forms a soluble combination of white indigo. The latter can then penetrate the fibre, and afterwards become fixed by reoxidation. This is the printer’s solid blue.
4. The finely ground, but not dissolved indigo, is placed upon the tissue in such conditions that it can be dissolved and reduced in place. This done, the fixing of the indigotine is effected by oxidation. This is the method for China blue orbleu faïence.
Without dwelling upon the details of these methods, we hasten to a consideration of the most important of all the applications of indigo:—
The Copperas Vat.—For dyeing cotton, the method of reduction found by experience to be the most convenient and practical is founded upon the action of the hydrate of the protoxide of iron in the presence of lime. The hydrated protoxide of iron is obtained from sulphate of iron (green vitriol, or copperas) with freshly burned lime. Certain precautions should be observed in the use of these materials. The copperas used for the preparation of these vats should be free from sulphate of copper, because the oxide of copper which would be formed in the vats rapidly oxidizes the reduced indigo, and causes its precipitation in the bath. The copperas ought not to contain red oxide of iron, nor sulphate of alumina. The coppery or oxidized vitriol may be purified by boiling the solution with pieces of iron, which precipitates the iron and neutralizes the oxide. The lime ought to be pure, containing no magnesia; when slacked lime has been exposed to the air, even for a short time, it absorbs carbonic acid, and becomes converted into chalk. The lime, therefore,should always be newly slacked. The ingredients, then, of a copperas vat are water, pure or purified green vitriol, indigo ground into a homogeneous impalpable paste, and pure and freshly slacked lime. The proportions used in different establishments are exceedingly variable. Those which answer for a laboratory vat, or a small vat used for precipitating the white indigo immediately for printing, are: indigo, one part; sulphate of iron, two parts; slacked lime, three parts. These proportions are not enough for the large vats used in dyeing pieces. In them it is necessary to make the quantities of lime and sulphate of iron larger than the theory of the vat requires. The excess of lime and hydrate of iron serve the purpose, whenever the vat is stirred, to repair the losses of indigo caused by its oxidation from contact with the air. Schutzenberger gives the proportions generally used by the dyers of France, as follows:—
Others, he says, use more lime than copperas, as in the following proportion:—
M. de Kæppelin, who is especially familiar with the cotton dyeing in Mulhouse, describes the ordinary vats for cotton dyeing as bound with iron, and placed on the level of the ground. They hold from 3,000 to 4,000 litres (1,055 gallons) of liquid. In preparing them the dyer fills them about three-quarters full of water, and pours in a milk of lime, prepared with 45 kilograms (100 lbs.) of freshly slacked lime; a fine liquid paste having been previously made from 15 kilograms (33 lbs.) ground in water. This is added to the lime in the vat by portions, the liquid in the vat being stirred up by a rake after each portion of the indigo paste has been added. The indigo becomes dissolved in about twenty-four hours, when the vat can be used. After describing the manner in which the frame, orchampignon, containing the goods to bedyed is arranged and immersed in the vat, this author continues: “It will be understood that the vat is composed according to the degree of intensity of the color which is sought to be obtained, and that hues more or less deep may be obtained by means of more or fewer repeated immersions of the fabric to be dyed. After each immersion thechampignonis lifted out of the vat, and the fabrics are left toungreenthemselves by contact with the air. (It must be observed that, although soluble indigo is called white, because it is without color when carefully prepared in the laboratory, the goods, when first taken from the ordinary vat, are of a green color.) Exposed to the air, the soluble indigo is precipitated in the state of blue indigo upon the fibres of the tissue. This oxidation, ordehydryzation, may be hastened by plunging the tissue into a vat containing a solution, very much diluted with water, chloride of lime, bichromate of potash, or sulphuric acid. The first two act as oxidizing agents; the last facilitates the restoring of the blue indigo by depriving it of the lime which is in excess in the solution of indigo which the tissue has imbibed from the vat.”
He adds further: “To facilitate the formation of blue indigo in the interior of the fabrics, the stuff to be dyed may be previously impregnated by a saline solution, which has the property of precipitating the white indigo from the alkaline solution, and of fixing itself more rapidly upon the tissue. Oxide of copper and oxide of manganese possess these properties in a high degree, and are used in many establishments to hasten the dyeing process, and produce an economy in raw materials. The pieces of cloth are placed in a solution of sulphate of copper, in the proportion of 15 to 20 grams to the litre (2.11 pints), and lightly thickened with starch. The fabrics, thus impregnated by a kind of mordant, before receiving the blue dye are first passed through a weak bath of milk of lime, which fixes the oxide of copper upon the tissue. The blues thus obtained are more intense, and have a peculiar lustre. This process is used in Austria and Germany, where cotton fabrics are printed on both sides of the tissue.”
Coming to the English authorities, Dr. Grace Calvert, inhis recent lectures before the Society of Arts, speaking of the cold vat for dyeing cotton, says: “The oldest, and still most generally employed method of preparing cold vats, consists of putting into a vat containing about 2000 gallons of water 60 lbs. of indigo, very finely powdered, 180 lbs. of slacked lime, and 120 lbs. of sulphate of protoxide of iron, or green vitriol (free from any trace of copper salt), the two latter substances being added from time to time. The greater part of the lime used unites with the sulphuric acid of the iron salt, to produce sulphate of lime or gypsum; and the liberated protoxide of iron removes the oxygen from the indigo, becoming converted into saline oxide, whilst the reduced indigo dissolves in the excess of lime employed.”
He adds the following facts, which may be of practical value:—
“Messrs. R. Schloesser & Co., of Manchester, have introduced within the last year or two a marked improvement, in the preparation of cold vats, which removes the great objections of the bulky precipitate of sulphate of lime, the formation of an oxide of iron, and the loss of indigo by its combination with the oxide of iron. The bath remaining much more fluid, the pieces are less apt to be spotted, and a better class of work is produced. To carry out their process, they add to the ordinary 2,000 gallon vat 20 lbs. of ground indigo, 30 lbs. of iron borings, 30 lbs. oftheir remarkable powdered zinc, and 35 lbs. of quicklime; the whole is stirred up from time to time, for twenty-four hours, when it is ready for use. If the bath is not considered sufficiently strong, a little more lime and zinc are introduced. The chemical theory of the process is, that the zinc, under the influence of the lime, decomposes the water, combining with its oxygen, and the hydrogen thus liberated removes oxygen from the indigo which then dissolves in the lime.”
An excellent description of the processes employed at Manchester, England, in preparing and working the copperas, or cold vat, is given in Ure’s “Dictionary of Manufactures.” “The ingredients necessary for setting the vat are copperas, newly slacked quicklime, and water. Various proportions ofthese ingredients are employed, as, for instance: 1 part by weight of indigo (dry), 3 parts of copperas, and 4 of lime; or, 1 of indigo, 2¹⁄₂₃ of copperas, and 3 of lime; or, 8 of indigo, 14 of copperas, and 20 of lime; or, 1 of indigo, ¾ of copperas, and 20 of lime; or 1 of indigo, 4 of copperas, and 1 of lime. The sulphate of iron should be as free as possible, from red oxide of iron, as well as sulphate of copper, which reoxidize the reduced indigo-blue. The vat, having been filled with water to near the top, the materials are introduced, and the whole, after being well stirred several times, is left to stand for about twelve hours. The chemical action which takes place is very simple. The protoxide of iron, which is set at liberty by the lime, reduces the indigo-blue; and the indigo, which is then dissolved by the excess of lime, forming a solution, which, on being examined in a glass, appears perfectly transparent and of a pure yellow color, and becomes covered, whenever it comes in contact with the air, with a copper-colored pellicle of regenerated indigo-blue. The sediment at the bottom of the vat consists of sulphate of lime, peroxide of iron, and the insoluble impurities of the indigo, such as indigo-brown in combination with lime, as well as sand, clay, &c. If an excess of lime is present, a little reduced indigo-blue will also be found in the sediment in combination with lime. The dyeing process itself is very simple. The vat having been allowed to settle, the goods are plunged into the clear liquor, and, after being moved about in it for some time, are taken out, allowed to drain, and exposed to the action of the atmosphere. While in the liquid, the fabric attracts a portion of the reduced indigo-blue. On now removing it from the liquid, it appears green, but soon becomes blue on exposure to the air, in consequence of the oxidation of the reduced indigo-blue. On again plunging it into the vat, the deoxidizing action of the vat does not again remove the indigo-blue which has been deposited within and around the vegetable or animal fibre, but, on the contrary, a fresh portion of the reduced indigo-blue is attracted, which, on removal from the liquid, is again oxidized like the first, and the color thus becomes a shade darker. By repeating this process severaltimes the requisite depth of color is attained. This effect cannot, in any case, be produced by one immersion in the vat, however strong it may be. The beauty of the color is increased by finally passing the goods through diluted sulphuric or muriatic acid, which removes the adhering lime and oxide of iron. After being used for some time, the vat should be refreshed or fed with copperas and lime, upon which occasion the sediment must first be stirred up, and then allowed to settle again, so as to leave the liquor clear. The indigo-blue, however, is in course of time gradually removed, and by degrees the vat becomes capable of dyeing only pale shades of blue. When the color produced by it is only very faint, it is no longer worth while using it, and the contents are then thrown away. In dyeing cotton with indigo, it seems to be essential that the reduced indigo-blue should be in contact with lime. If potash or soda are used in its place, it is impossible to obtain dark shades of blue.”
The application of indigo-blue to wool and woollen tissues is always made by means of vats, which have special names; as, the pastel or woad vat, the urine vat, German vat, molasses vat, &c. The reduction orhydrogenationof the indigo-blue is the result of a peculiar fermentation, which is developed within an alkaline liquor by means of nitrogenized substances and bodies rich in sugar or hydrocarbonized substances. It is known that in these conditions, especially where the temperature is slightly raised, the sugar is converted into butyric acid, and at the same time carbonic acid and hydrogen are set free. We find here the source of the nascent hydrogen which fixes itself upon the indigo-blue, and transforms it into white indigo, which is soluble in the alkalies of the vat. It has recently been observed that the butyric fermentation proceeds from the development of minute infusoria. These animalculæ live without any supply of oxygen, and, in fact, are killed in its presence. They therefore live at their ease in the vat of reduced indigo, where no oxygen is permitted to enter.
The ingredients most usually employed for furnishing thehydrocarbonaceous substances for fermentation are bran and ground madder, although molasses is sometimes used. The nitrogenized material is found in the woad or pastel, which is often added in very large proportions to the fermenting vats. It is observed by the chemists who have studied this subject most carefully, that the preparation of vats, founded upon the principle of fermentation, does not repose upon principles so sure and constant as those of the copperas vat, and that many unforeseen accidents interpose to disturb the work of an inexperienced dyer. The phenomena in fermentations are often complex. It is admitted that in these phenomena theory has not said its last word, and that empiricism is often more fortunate than science. In conducting the operations of the warm fermenting vat, the conceit of the practical dyer, so often remarked upon, is not without foundation. By practical experience and the traditions of his art he has acquired a knowledge of the almost insensible modification in conditions which can change or arrest the chemical reaction. It is the knowledge of the workman, a knowledge almost instinctive, which can never be communicated to the books, and which is most respected by those most profoundly informed in theory.
The Woad or Pastel Vat.—In former times woad, already referred to, was the only material known to the dyers of Europe for producing the blue color of indigo. For dyeing wool, the use of woad, now abandoned wholly in cotton dyeing, has been retained to the present day, generally for the purpose of exciting fermentation, and without regard to its effect in imparting color to the material to be dyed; for the woad grown in England, and used in the dye-houses of that country, contains no trace of coloring matter. The woad, or pastel, grown in the warmer districts of France contains about two per cent of indigotine, which is regarded in that country as an important addition to the coloring material, especially for improving the tone of the color. Various substitutes, such as rhubarb leaves, turnip and carrot tops, and weld, have been tried, but without advantage, with the exception, perhaps, of weld, which is still used by some dyers. Some chemists regard the use of woad asthe remnant of a prejudice; but the better opinion is, that this material possesses peculiar fermentiscible qualities, whose exact action science has yet to resolve.
According to Schutzenberger, the most recent and highest French authority, the dimensions of the pastel vat are about 6½ feet in diameter, by 9 in depth. 100 kilograms (221 lbs.) of pastel, in balls, is placed in the vat, which is then filled with boiling water. To this is added 10 kilograms (22 lbs.) of madder, 3 to 4 kilograms (about 6½ to 8¾ lbs.) of bran, and 4 kilograms of quicklime, which has been slacked, and in the form of abouilli. Sometimes weld is also added. After three hours of rest, the vat is well raked, and the operation is repeated every three hours. There is gradually developed a characteristic ammoniacal vapor, and a blue scum, with veins of deeper blue, forms on the surface; and the liquid, when agitated in the air, rapidly becomes blue. These symptoms indicate the dissolution of the indigotine of the woad; then there is added 10 kilograms (22 lbs.) of indigo which has been previously ground in water, and the vat is stirred. If the fermentation appears to be proceeding too actively, which is recognized by the disengagement of gases, it is checked by the addition of a proper dose of lime. On the other hand, the fermentation is made more active by increasing the dose of bran. The first dyes are not so good as those subsequently obtained, as the woad absorbs from the bath certain brown or yellow materials, kept in solution, and furnished as well by the pastel and madder as by the indigo itself. 100 kilograms of wool require from 8 to 12 kilograms of indigo. The vat is kept up by successive additions of indigo and lime, made in the evening.
Another kind of pastel vat, prepared much like the last, receives an addition of a dose of potash. M. de Kæppelin describes it as the one at present in general use in France. Into a vat containing from 3,000 to 4,000 litres (791 to 1,055 gallons) there is placed 75 kilograms (166 lbs.) of pastel in loaves, or which has undergone a kind of fermentation; or, what is preferable, 80 to 100 kilograms (176 to 221 lbs.) of pastel or woad gathered without fermentation, and 10 kilograms (22 lbs.) ofindigo, ground to a paste with water. This mixture is well stirred, and there is added 4 kilograms (about 9 lbs.) of Avignon madder, and the same quantity of carbonate of potash. After the vat has been well raked there is added 2 kilograms (4½ lbs.) of slacked lime, and some pails of bran. The vat is well covered, either with a wooden lid, or woollen cloths. The fermentation is allowed to proceed, and after five or six hours the vat is uncovered and raked with much care for half an hour. This operation is repeated every three hours, until it is recognized that the indigo is well dissolved. In this case the bath ought to be of a beautiful yellow color, and be covered with a light blue irised film, veined with yellow at the least movement given to the liquid. If the fermentation proceeds too rapidly, a little lime is added to moderate it.
For keeping up a vat like this, and to obviate the different inconveniences to which it is subject, the dyer sometimes adds lime, or sugar, and carbonate of ammonia, sometimes madder, or bran, or even tartar-lees. These last additions are made to saturate the excess of lime which the vat contains. In this case the yellow veins and the beautiful blue scum which cover the surface disappear, or become pale; a piquant odor is disengaged, and the liquor becomes blackish. When lime or sugar are added, it is for the purpose of retarding the fermentation of the woad. Sugar might even entirely take the place of pastel for effecting the reduction of the indigo, and many establishments in France are commencing to use it for this purpose. A good vat, well supplied with successive additions of indigo, pastel, bran, and madder, in proportions necessary to effect and prolong the fermentation necessary for the dissolution of the indigo, may be kept up many years.
Schutzenberger observes that the vats of fermentation are subject to certain maladies, the two most frequent of which are due, one to an excess, and the other to an insufficient quantity of lime. “In the first case, the liquid takes a tint more and more free of color, loses itsfleurée(surface scum) and odor; the fermentation is then arrested by the precipitation of the active matters. This inconvenience is remedied, if seen in time, byadding sulphate of iron, which eliminates the too great excess of lime. In the second, the fermentation becomes too active, passes into a putrid fermentation, and the liquid assumes a reddish tint; a fabric dyed with indigo in this state becomes very soon discolored. The sole means of safety is to heat the bath up to 90° and to add lime. If this does not accomplish the purpose of arresting the putrefaction the vat is lost.”
The following account of the method of dyeing woollen goods with indigo by means of the woad vat is given by Dr. Ure, as that carried on in Yorkshire, the great centre of the woollen manufacture of England.
“The dye-vats employed are circular, having a diameter of six feet six inches, and depth of seven feet, and are made of cast-iron five-eighths of an inch in thickness. They are surrounded by brickwork, a space of three inches in width being left between the brickwork and the iron, for the purpose of admitting steam, by means of which the vats are heated. The interior surface of the brickwork is well cemented. In setting a vat the following materials are used: 5 cwt. of woad, 30 lbs. of indigo, 56 lbs. of bran, 7 lbs. of madder, 10 quarts of lime. The woad supplied to the Yorkshire dyers is grown and prepared in Lincolnshire. It is in the form of a thick, brownish yellow paste, having a strong ammoniacal smell. The indigo is ground with water in the usual manner. The madder acts in promoting fermentation, but it also serves to give a reddish tinge to the color. The lime is prepared by putting quicklime into a basket, then dipping it in water for an instant, lifting it out again, and then passing it through a sieve, by which means it is reduced to a fine powder, called by the dyersware. The vat is first filled with water, which is heated to 140° F., after which the materials are put in, and the whole is well stirred until the woad is dissolved or diffused, and it is then left to stand undisturbed overnight; at six o’clock the next morning the liquor is again stirred up, and five quarts more of lime are added; at ten o’clock five pints of lime are again thrown in, and at twelve o’clock the heat is raised to 120° F., which temperature must be kept up until three o’clock, when another quart of limeis introduced. The vat is now ready for dyeing. When the process of fermentation is proceeding in a regular manner, the liquid, though muddy from insoluble vegetable matter in suspension, is of a yellow or olive yellow color; its surface is covered with a blue froth or copper-colored pellicle, and it exhales a peculiar ammoniacal odor; at the bottom of the vat there is a mass of undissolved, matter of a dirty yellow color. If there is an excess of lime present, the liquor has a dark green color, and is covered with a grayish film, and, when agitated, the bubbles which are formed agglomerate on the surface, and are not easily broken. Cloth dyed in a liquid of this kind loses its color on being washed. This state of the vat is remedied by the addition of bran, and is of no serious consequence. When, on the other hand, there is a deficiency of lime, or, in other words, when the fermentation is too active, the liquor acquires first a drab, then a clay-like color; when agitated, the bubbles which form on its surface burst easily, and when stirred up from the bottom with a rake it effervesces slightly, orfrits, as the dyers say. If the fermentation be not checked at this stage, putrefaction soon sets in, the liquid begins to exhale a fetid odor, and when stirred evolves large quantities of gas, which burns with a blue flame on the application of a light. The indigo is now totally destroyed, and the contents of the vat may be thrown away. No further addition of woad is required after the introduction of the quantity taken in first setting the vat, the fermentation being kept up by adding daily about four pounds of bran with one quart or three quarts of lime. Indigo is also added daily for about three or four months. The vat is then used for the purpose of dyeing light shades, until the indigo contained in it is quite exhausted, and its contents are then thrown away.”
This author adds: “Woollen cloth, before being dyed, is boiled in water for one hour, then passed immediately under cold water. If it be suffered to lie in heaps after being boiled it undergoes some change, which renders it afterwards incapable of taking up color in the vat. In dyeing, the cloth is placed on a net-work of rope attached to an iron ring, which is suspended by four iron chains to a depth of about three feet beneath the surface of theliquor. The cloth is stirred about in the liquor by means of hooks for about twenty or thirty minutes. It is then taken out and well wrung. It now appears green, but, on being unfolded and exposed to the air, rapidly becomes blue. When the vat has an excess of lime the cloth has a dark green color when taken out. It is then passed through hot water, and dipped again if a darker shade is required.”
The Indian Vat.—This presents much analogy to the woad vat, as the fermentation of vegetable matters effects the transformation of the indigo-blue. According to Dr. Calvert, the Indian vat, probably so called from its origin in the East, is taking the place in England of the old woad vat for dyeing wool and woollens. He describes its preparation as follows: 8 lbs. of powdered indigo is added to a bath containing 3½ lbs. of bran, 3½ lbs. of madder, and 12 lbs. of potash, which is maintained for several hours at a temperature of 200° F. It is then allowed to cool to 100° F., when fermentation ensues. After about forty-eight hours the indigo is rendered soluble, being reduced by the decomposition of the sugar and other products contained in the bran and the madder root during the process of fermentation. The distinguishing feature of this vat is the use ofpotash. The Indian or potash vats are spoken of by the best authorities as more easy to manage than the woad vat. They are less subject to accidents, and yield their coloring material more readily to the fibre, while three times as much wool can be dyed in the same time. On the other hand, they do not last so long, and require to be renewed at the end of twenty-five or thirty days. Besides, the fibres dyed in the potash vat have a darker shade than those dyed in the woad vat, owing to the large quantity of the coloring matter of the madder dissolved by the potash, which becomes fixed on the stuff with the indigo-blue.
The Urine Vat, but little used except for domestic dyeing, is founded upon the same principles as the other fermenting vats. This excretion, when putrefied, contains at the same time the nitrogenized principles which work as ferments and the alkali in the form of ammonia necessary for dissolving the indigo.
According to Dr. Calvert, improvements have been made oflate years in the fermenting indigo vats by which the expense of madder is avoided. They are now prepared by adding to water, at a temperature of 200° F., 2 buckets of bran, 26 lbs. of soda crystals, 12 lbs. of indigo, and 5 lbs. of slacked lime. After five hours the bath is allowed to cool to 100° F., when fermentation ensues, and the indigo is dissolved in the alkali. This is, in fact, the German vat, soda taking the place of the potash, and the only fermenting material consisting of bran.
The German Vatis largely used by the dyers in the north of France, and is considered as more advantageous than the Indian vat, because the employment of soda is more economical than that of potash, while the vat can be maintained as long as two years. The vats used by them are prepared as follows: The water is heated to a temperature of 95°, and receives 20 pails of bran, 11 kilograms (about 24 lbs.) of crystals of carbonate of soda, 5.5 kilograms (11 lbs.) of indigo, and 4½ lbs. of slacked lime. After twelve hours, the temperature having been kept at 40° or 50°, fermentation commences, the liquid becomes of a greenish blue color, and disengages bubbles of gas. Indigo, soda, and lime are put in from time to time in the proportions above indicated, and also from six to eight pounds of molasses. At the end of the third day the vat is fit for use.
M. de Kæppelin, writing in. 1864, informs us that the reduction of indigo by means of molasses, is at present largely employed in the great establishments for dyeing woollen cloth at Sedan, Louviers, and Elbœuf.
The vat used is of very large dimensions, and from twenty-two to twenty-six pounds of indigo are dissolved in it; an equal weight of molasses is used, and three or four times the same weight of potash made caustic by a proportionate addition of lime.
The space reserved for this subject in our present paper will not permit us to enter upon a description of the processes used in the American dye-houses. This, as well as the applications of indigo in printing, and the uses of sulphate of indigo, must be deferred to another number.
Let us, in concluding the first part of our paper, at the risk ofrepetition, bring out in bolder relief a statement which presents the philosophy of all the various processes of the indigo vat, and at the same time, a conclusive argument for the use of this material, in preference to all cheaper substitutes. Indigo cannot enter into a fibre until it is dissolved. It cannot be dissolved so long as it is in a blue state. When reduced by any of the processes above described to the white state, it is easily dissolved, and can enter the pores of the fibre. Upon exposure to the oxygen of the air it takes up an equivalent of oxygen; it returns to the blue state, and, being then insoluble, it cannot be washed away from the fabric, and being saturated with oxygen it cannot be changed by air or light. This theory of the application of indigo involves a lesson to manufacturers, dealers, and consumers, especially of woollen fabrics. The theory, as well as experience, dating back to the dawn of the textile arts in the East, establishes that this material is incalculably superior to any other, in permanence at least, for imparting to woollen fibre a blue color, or as a foundation for most of the darker colors. By far the largest proportion of all cloths are of dark colors,—blue, black, green, brown, gray, or mixed,—and can advantageously receive in all or a portion of the fibre constituting them a direct dye or bottom for other dyes from indigo. It may be safely stated that, as a whole, no cloths in the world are manufactured from such good wool as those produced in the United States. We might expect that the shoddy goods of Yorkshire should be further falsified by fugacious dyes; but is it not a shame that our admirable wool should be deprived of half its value by parsimony in dyeing? The slightest shortcomings in dyeing are revealed in wear. The writer cannot forbear referring to an illustration directly before his eyes. He is wearing a garment, reduced now to the retired service of an office coat, made of an admirable cheviot cloth of American manufacture. The cloth originally was selected not only for its excellent texture, but as an illustration of philosophical principles applied in the formation of color. The tissue was made by weaving three yarns of distinct colors,—blue, yellow, and red. Either of those hues alone would have beenglaring and conspicuous, but, by the law of color, the combination of blue, red, and yellow makes black, and the new cloth at a distance had the effect of a dark mixture. Upon exposure to ordinary wear, the yellow and red have retained their pristine hues; the blue, not being indigo dyed, has faded; and the original dark mixture, although sound in fabric, has become of a yellowish brown. The extra expense of a permanent dyeing material forms so small a proportion of the whole cost of a finished garment, that it ought not to be generally spared. The reform cannot be made by the manufacturers; it must be made by the dealers, and especially by that class of producers which has risen in our day into such great importance,—the manufacturers of ready-made clothing. If they would demand of the manufacturers, and furnish to their customers cloths more permanently dyed, it would be another step in the direction to which these establishments are tending,—the supply of the chief portion of the woollen clothing of the people. The manufacturers would gladly aid them; for it is the growing sentiment of American manufacturers that all their productions should be, in the proverbial phrase adopted from the dye-house, as expressing the highest excellence,—true blue.