It is with the vegetable coloring matters, however, that the greatest attention must be paid to the many conditions and properties of mordants. Bi-chromate of potash is largely used as a mordant for logwood and fustic for blues, blacks, browns and a variety of shades of color. Bi-chromate of potash, alum and oxalic acid as mordant on wool produce with logwood a very fine navy blue, but one that is not very fast to light. Sulphate of copper is the mordant most largely used with logwood for making black on cotton. These mordants are used almost exclusively for the wool dyes. In dyeing wool, either raw, woven or as yarn, care has to be taken that the wool is thoroughly free from grease before being mordanted. This is done by passing it through either soap, sal soda or soda ash and then thoroughly rinsing to free it from the alkali solution. If this is not done unevenness in the dyeing is caused, as well as a rubbing off of the color. When the dyer is given a shade to match he has to take into con sideration the degree of fastness required, as where goods have to be heavily fulled, unless the colors are sufficiently fast, they will full out and be spoiled. In this case only such dyes can be used as will stand this process. The quantity of dye to be used depends on the class of wool to be dyed, as the finer the quality of the wool the more dyestuff it takes to produce the same shade. The dyer also has to study to produce the result at the lowest possible cost, both for labor and dyestuff. Machines are now manu factured which economize in the labor and a large quantity of goods are dyed at one time It would be generally supposed that where the dyer carefully proportioned out his dyestuff to the weight of the material to be dyed and ob served every care in reference to the mordant and heat that the shades would come out alike. However, this is not the case, and with the greatest amount of care the shades will vary and it is necessary to use extra skill after the shades get off the pattern to bring them again to the shade required. The dyer, knowing full well that owing to difference in the water and the stock in the goods, besides conditions that are not always understood, that the shade is apt to vary, begins his operation with a minimum quantity of the dyestuff and if he finds that he is not up to the shade required, he adds such dyestuff as is necessary to give the desired result. In fact, making the shade right when it is once off the pattern requires the highest skill on the part of the dyer. The dyeing of wool is the result of a chemical combination. On the other hand, the dyeing of cotton is a fixation of a colored substance in the pores of the cotton. Cotton is dyed in the raw state, pieces and yarns, and the amount of dye used to produce a given shade also varies somewhat according to the quality of the staple. In using colors re quiring a mordant sumac and antimony are used, and the amount employed is governed by the depth of the shade required.
Dyeing of Mixed Fabrics.— The coloration of textile fabrics composed of more than one kind of material generally requires two or more processes, as the plan pursued in dyeing wool is seldom capable of fixing the color upon cot ton. The customary plan followed is to im merse the fabric in the requisite baths to dye the wool and then to treat the dyed material in the manner found suitable for cot ton. Occasionally the woolen thread of the cloth is dyed of one color and thereafter the cotton is treated so as to acquire a different shade or color. With some of the coal-tar colors mixed fabrics can be dyed in one bath, thus saving much time. The dyer is now able to produce by combination of different dyes a great variety of rich shades on mixed fabrics, and even to dye two shades in the same fabric by first dyeing the wool in the hot bath with an acid dye, then cooling down his bath and adding his cotton dye and dyeing the cotton another shade from what was produced on the wool. In dye ing silk care has to be taken to free the silk from all gums, and this is done by boiling off in a soap bath. Most of the dyeing is done direct and under the boil.
In imparting deep indigo blue to woolen cloth and yarn a vat six or seven feet in diameter and eight to nine feet in depth is nearly filled with water, along with from 18 to 22 pounds of indigo finely ground in water, 10 to 20 pounds of madder, 7 to 9 pounds of bran and 9 pounds woad. After boiling and the addition of seven or eight pounds of lime to form the alkaline liquid necessary to hold the indigo solution, the whole is well closed over with tightly-fitting wooden covers. Within 24
hours the putrid fermentation of the woad and the bran abstracts the oxygen from the blue indigo until it assumes a yellowish color, and the, solution then contains indigo white. If woolen cloth or yarn is.now dipped in this liquid it comes out of a yellow tint from the attachment of the white indigo. But when exposed to the air the oxygen immediately begins to act on the white indigo, combining with it to form oxidized or blue indigo, and as the process of oxidation continues the yarn or cloth becomes first of a greenish and then of a blue color. If the cloth be again soaked in the yellowish solution and subsequently exposed to the air the depth of the blue color may be increased, step by step, till it arrives at that deep shade of blue so well known.
In the dyeing of cotton with indigo the vat is prepared differently. The indigo is first ground into a thin paste with water and afterward placed in a vat with protosulphate of iron and milk of lime. The lime (CaO) takes the sul phuric acid (S0.)from the sulphate of iron (Fe0S0.) forming sulphate of lime (CaOSOa), and liberating the protoxide of iron (Fe0), which rapidly abstracts the oxygen from the blue indigo, reducing it to white indigo, and the latter dissolves in the excess of lime present in the vat, yielding a colorless solution. When cotton cloth or yarn is dipped in this it comes out of the vat almost colorless, but on exposure to the air the indigo becomes reoxidized and the cloth passes to a green and ultimately to a deep blue shade. The cloth or yarn is then washed in water and afterward soaked in a very dilute sulphuric acid to remove any oxide of iron remaining attached and rewashed in water, when the blue color becomes more bright and clear. Fast fulling colors dyed either in the wool yarns or pieces are usually dyed with the alizarine colors on account of their being fast to fulling and light. These are usually mordanted with bi-chromate of potash and cream of tartar for one and a half hours at the boiling point. Then they are thoroughly rinsed in cold water and finished in another bath with the alizarine colors. Owing to the great affinity existing between the alizarine colors and the mordanted wool, great care has to he taken to enter the bath at a low temper ature and very gradually bring to the boil to ensure the goods being dyed even. Extra care must also be taken that no more alizarine is added than is necessary to produce the shade.
Cotton is now largely dyed direct. Formerly dyers were obliged to give a number of baths and even then were not able, in a great many cases, to secure the brilliant shades that are now dyed in one operation. The color simply being fixed in the pores of the cotton, it is more diffi cult to secure a fast color on this fibre than on wool. As in the case of wool, dyeing machines are now manufactured by which the cotton is dyed both in the raw state, yarns and pieces, which economize in the labor and enable the dyer to produce better results both as to shade and fastness. During the last few years, there has been a large addition to the coal tar dyes, thus giving cotton dyers a much better oppor tunity to produce brighter and faster colors.
The yarns for carpets are dyed almost ex clusively with the coal tar dyes. This is done direct by entering them in the dye bath, which has previously had added the color, with the proper proportion of sulphuric acid and glauber salt and gradually brought to the boil, being turned by hand. The bath is generally exhausted in about three-quarters of an hour. The yarns as furnished to the dyer are frequently of a mixed material which is dark in color, and in this case he must choose the most brilliant of dyes to give the required brightness of shade. For the finer grades of carpets, the color must thoroughly penetrate and in matching shades the dyer usually cuts his yarn and matches from the centre.
Bibliography.—aBadische Anilin and Soda Fabrikp (in (Manual of Garment Dyeing,' 1911) ; Beaumont's 'Colors in Woven (1912) • Carter's (Bleaching, Dyeing and Fin ishing Flax, Hemp and Jute (1911); Huebner's (Bleaching and Dyeing of Vegetable Fibrous Materials) (1912) ' • Matthew's 'Labora tory Manual of (1900) ; Fellow's and Dyeing) (1913) ; Wood's (Chemistry of Dyeing) (1913).
F. H. Panscotr, Expert in Dyes and Dyeing, Philadelphia