Klauder-Weldon Dyeing Machine
Klauder-Weldon Hank-dyeing Machine.--This is illustrated infigure 15, which shows the latest form. It consists of a half-cylindrical dye-vat built of wood. On a central axis is built two discs or rod carriers, which can revolve in the dye-vat, the revolution being given by suitable gearing which is shown at the side of the machine. On the outer edge of the discs are clips for carrying rods on which one end of the hanks of yarn is hung, while the other end is placed on a similar rod carrier near the axle. The revolution of the discs carries the yarn through the dye-liquor contained in the lower semi-cylindrical part of the machine previouslyalluded to. At a certain point in every revolution of the discs the rods carrying the yarns are turned a little; this causes the yarn to move on the rods, and this motion helps to bring about greater evenness of dyeing. The most modern form of this machine is provided with an arrangement by means of which the whole batch of yarn can be lifted out of the dye-liquor. Arrangements are made by which from time to time fresh quantities of dyes can be added if required to bring up the dyed yarn to any desired shade. This machine works well and gives good results. Beyond the necessary labour in charging and discharging, and a little attention from time to time as the operation proceeds, to see if the dyeing is coming up to shade, the machine requires little attention.
Many other forms of hank-dyeing machine have been devised. There is Corron's, in which an ordinary rectangular dye-vat is used. Round this is a framework which carries a lifting and falling arrangement that travels to and fro along the vat. The hanks of yarn are hung on rods of a special construction designed to open them out in a manner as nearly approaching hand work as is possible. The machine works in this way. The lifting arrangement is at one end of the vat, the hanks are hung on the rods and placed in the vat. Then the lifter is set in motion and moves along the vat; as it does so it lifts up each rod full of yarn, turns it over, opening out the yarn in so doing, then it drops it again in the vat. When it has travelled to the end of the vat it returns, packing up the rods of yarn in so doing, and this motion is kept up until the dyeing is completed. This machine is very ingenious.
A type of machine which has been made by several makers consists of an ordinary rectangular dye-vat surrounded with a framework carrying a number of sets of endless chains, the links of which carry fingers. The hanks of yarn are hungon rods at one end of which is a tooth wheel that when in position fits into a rack on the side of the vat. The action of the machine is this, the hanks are hung on the rods and placed at the entrance end of the vat, by the moving of the chains it is carried along the vat and at the same time revolves, thus turning over the yarn, which hangs in the dye-liquor; when it reaches the opposite end of the vat, the rod full of yarn is lifted out, carried upwards and then towards the other end of the vat when it is again dropped into the dye-vat to go through the same cycle of movements which is continued until the yarn is properly dyed.
Piece Dyeing Machines.--Wherever it is possible it is far more preferable to dye textile fabrics in the form of woven pieces rather than in the yarn from which they are woven. During the process of weaving it is quite impossible to avoid the material getting dirty and somewhat greasy, and the operations of scouring necessary to remove this dirt and grease has an impairing action on the colour if dyed yarns have been used in weaving it. This is avoided when the pieces are woven first and dyed afterwards, and this can always be done when the cloths are dyed in one colour only. Of course when the goods are fancy goods containing several colours they have to be woven from dyed yarns.
The most common form of machine in which pieces are dyed is the jigger, commonly called the jig, this is shown in figure 16. It consists of a dye-vessel made long, sufficiently so to take the piece full width, wide at the top, narrow at the bottom. At the top on each side is placed a large winding roller on which the cloth is wound. At the bottom of the jig is placed a guide roller round which passes the cloth. In some makes of jigs there are two guide rollers at the bottom and one at the top as shown in the illustration, so that the cloth passes several times through the dye-liquor. In working the cloth is first wound on one of the rollers thenthreaded through the guide rollers and attached to the other winding roller. When this is done dye-liquor is run into the jig, and the gearing set in motion, and the cloth wound from the full on to the empty roller. With the object of keeping the piece tight a heavy press roller is arranged to bear on the cloth on the full roller. When all the cloth has passed from one roller to the other it is said to have been given "one end". The direction of motion is now changed and the cloth sent in the opposite direction through the jig and the piece has now received another "end". This alternation from one roller to the other is continued as long as is deemed necessary, much depending on the depth of colour which is being dyed, some pale shades may only take two or three ends, deeper shades may take more. When dyeing wool with acid colours which are all absorbed from the dye-liquor, or the bath is exhausted, it is a good plan to run the pieces several ends so as to ensure thorough fixation of the dye on the cloth.
Dye-jiggers
It is not advisable in working these jigs to add the whole of the dye to the liquor at the commencement, but only a part of it, then when one end is given another portion of the dye maybe added, such portions being always in the form of solution. Adding dyes in powder form inevitably leads to the production of colour specks on the finished goods. The reason for thus adding the dye-stuff in portions is that with some dyes the affinity for the fibre is so great that if all were added at once it would be absorbed before the cloth had been given one end, and, further, the cloth would be very deep at the front end while it would shade off to no colour at the other end. By adding the dye in portions this difficulty is overcome and more level shades are obtained, but it is met with in all cases of jigger dyeing. It is most common in dyeingwool with basic dyes like Magenta, Auramine, Methyl Violet or Brilliant Green, and with acid dyes like Acid Green, Formyl Violets, Azo Scarlet or Acid Yellow.
Dye-jigger in Section
Some attempts have been made to make jiggers automatic in their reversing action, but they have not been successful owing to the greatly varying conditions of length of pieces, their thickness, etc., which have to be dyed, and it is next to impossible to make all allowances for such varying conditions.
Wince Dye Beck
In figure 17 is shown the jig in section, when the working of the machine can be more easily traced.
The Jig Wince or Wince Dye Beck.--This dyeing machine is very largely used, particularly in the dyeing of woollen cloths. It is made by many makers, and varies somewhat in form accordingly. Figures 18 to 21 show three forms by different makers. In any make the jig wince or wince dye beckconsists of a large rectangular, or in some cases semi-cylindrical, dye-vat. Probably the best shape would be to have a vat with one straight side at the front, and one curved side at the back.
Wince Dye Beck
In some a small guide roller is fitted at the bottom, under which the pieces to be dyed pass. Steam pipes are provided for heating the dye-liquors. The beck should be fitted with a false bottom, made of wood, perforated with holes, or of wooden lattice work, and under which the steam pipes are placed. The object being to prevent the pieces fromcoming in contact with the steam pipes, and so preventing the production of stains. Above the dye-vat and towards the back is the wince, a revolving skeleton wheel, which draws the pieces out of the dye-vat at the front, and delivers them into it again at the back. The construction of this wince is well shown in the drawings. The wince will take the pieces full breadth, but often they are somewhat folded, and so several pieces, four, five or six, can be dealt with at one time. In this case a guide rail is provided in the front part of the machine. In this rail are pegs which serve to keep the pieces of cloth separate, and so prevent entanglements. The pieces are stitched end to end so as to form an endless band. When running through the vat they fall down in folds at the back part of the beck, and are drawn out from the bottom and up in the front. Each part thus remains for some time in the dye-liquor, during which it necessarily takes up the dye.
Plush Fabric Dyeing Machine
Figures 18 and 19 show forms of these wince dyeing machines, constructed of wood, and very largely used in the dyeing of woollen cloths. They are serviceable forms, and give very good results, being suitable for all dyes.
Figure 20 is a form of machine better adapted than the precedingfor the dyeing of plush fabrics. In this kind of cloth it is important that the pile should not be interfered with in any way, and experience has shown that the winces of the form shown in figures 18 and 19 are rather apt to spoil the pile; further, of course, plush fabrics are dyed full breadth or open. In the wince now shown all troubles areavoided, and plush fabrics can be satisfactorily dyed in them.
Copper Cased Dye Beck. Mather & Platt.
Figure 21 shows a dye-bath built of iron, cased with copper, suitable for dyeing most colours on woollen cloths.
Read Holliday's Hawking Machine
In the jig and wince dyeing machines the pieces necessarily are for a part of the time, longer in the case of the jigger than in that of the wince, out of the dye-liquor and exposed to the air. In the case of some dyes, indigo especially, this is not desirable, and yet it is advisable to run the cloth open for some time in the liquor so as to get thoroughly impregnated with the dye-liquor.
The so-called hawking machine, figure 22, is an illustration of Read Holliday's hawking machine, made by Messrs. Read Holliday & Sons, of Huddersfield. There is the dye-vat as usual; in this is suspended the drawing mechanism, whose construction is well shown in the drawing. This is a pair of rollers driven by suitable gearing, between which the cloth passes, and by which it is drawn through the machine. A small roller ensures the cloth properly leaving the large rollers,then there is a lattice-work arrangement over the pieces are drawn. In actual work the whole of this arrangement is below the surface of the dye-liquor in the vat. The piece to be dyed is threaded through the machine the ends stitched together, then the arrangement is lowered into the dye-vat and set in motion, whereby the cloth is drawn continuously in the open form through the dye-liquor, this being done as long as experience shows to be necessary. This hawking machine will be found useful in dyeing indigo on wool, in mordanting and dyeing wool with the Alizarine series of dyes.
The various methods which are used in dyeing wool have, of course, underlying them certain principles on which they are based, and on the observance of which much of the success of the process depends. Sometimes these principles are overlooked by dyers, with the result that they do not get good results from their work. It must be obvious to any person with any technical knowledge that all processes of dyeing either wool or silk, or cotton or any other fibre, must take into consideration the properties of the fibre on the one hand, and that of the dye-stuff on the other. Wool must be treated differently from cotton, a process of dyeing which gives good results with the latter fibre would lead to nothing but disastrous effects with wool or silk; on the other hand, processes are used in the dyeing of wool which could not be possibly used for cotton on account of the very different properties of the fibre.
A few words as to the properties of wool as far as they relate to the methods of dyeing may be of use. Wool has the property of resisting the action of acids in a great degree, so that it may be treated with even strong acids with impunity. On the other hand, alkalies and alkaline solutions have strong action on it; the caustic alkalies rapidly dissolve wool, and their use must be avoided in all cases of dyeing this fibre. The carbonates of the alkalies have not so strong an action, and therefore may be used in moderation; nevertheless, toostrong solutions of these should not be used. Soap has no disintegrating action on wool, and soap solutions may be used whenever necessary for cleansing or dyeing wool. Ammonia has no action on wool, and it may be used in place of soap if desired. There is one feature of wool that must be alluded to here, and that is its felting property. When wool is boiled with water and is handled a good deal, the fibres clot or felt together into a firm coherent mass. This should be avoided as much as possible, and when wool is cleansed and dyed in the loose condition it is absolutely necessary that every care be taken to avoid felting. This condition is much influenced by the temperature and the condition of the bath in which the wool is being treated, too high a temperature or too prolonged a treatment tends to increase the felting, therefore in dyeing wool prolonged treatment at the boil must be avoided.
Further, the condition of the bath has some influence on this point; it is found that an alkaline bath tends to considerably increase the felting properties of the wool, and on this account dyers invariably avoid the use of both the caustic and carbonated alkalies. Strong soap liquors have also some influence in the direction of increasing the felting, therefore soap should not be used if it can possibly be done without. Ammonia has not so strong a felting action as the other alkalies. Acids, on the other hand, exert a retarding action on the felting of the wool, and this is a matter of some interest and importance in the dyeing of wool, as an acid condition of the bath is necessary for dyeing by far the great majority of colouring matters on this fibre. Alkaline salts, such as Glauber's salt and common salt, exert little or no influence on this felting property, and can be added to dye-baths with impunity, and in many cases with good effect, so far as the quality of dyeing is concerned.
So far as the properties of the wool are concerned, it is seenthat an acid condition of the dye-bath will work better than an alkaline condition, and wherever it is possible to use acids such should be added.
What has been said in regard to wool is equally true of all fibres derived from animals in the same way as wool is, such as horse-hair, fur of rabbits, hares and other animals, although, of course, there are some minor differences between different furs in their resistance to the action of acids and alkalies.
The next feature that influences the methods of dyeing wool is the varying properties of the dye-stuffs, or colouring matters. It is obvious that those which, like Magenta or Saffranine, have a strong affinity for the wool fibre must be dyed differently from those which, like Alizarine and Gambine, have no direct affinity for the wool fibre, and, further, which require the aid of mordants before they can be dyed, and on the character of which mordants the colour that is fixed on the fibre depends.
The dye-stuffs, independently of the question whether they be derived from natural sources or be of artificial origin, may be roughly divided into five groups, some of which may also be subdivided again as will be shown later on. These groups may be named the (1) Neutral, (2) Basic, (3) Acid, (4) Mordant, and (5) Indigo dye-stuffs. The first two classes are practically dyed in the same way; but as there is a great difference in the chemical composition of the colouring matters comprised in them, it will be best to consider them separately.
First Method.--This method is used in applying the now large and increasing group of azo dye-stuffs, which are characterised by being able to dye unmordanted cotton from a simple boiling bath. The dye-stuffs that are applied by the method now to be described include such as Benzopurpurine, Chrysamine, Chrysophenine, Titan red, Titan yellow, Benzo brown, Diaminered, Diamine brown, Diamine blue, Congo blue, Congo red, etc. The dyeing is done in a bath at the boil. If the bath contained only the dye-stuffs there would be a liability for the dyeing to be uneven, to prevent which a saline compound, such as salt, is added. Taking it all round, salt is the best body to add as it suits all colours very well indeed. Then come Glauber's salts; borax and phosphate of soda can also be used, but, owing to their slight alkaline properties, they are not so good as the neutral salts, like the two first named. When these colouring matters are dyed on cotton some of them dye best in a bath containing potash or soda, but these bodies, for reasons previously pointed out, are not available in wool dyeing, and should never be used. Wool dyes best in a slightly acid bath, and this may be taken advantage of in dyeing the yellows and blues of this group by adding a small quantity of acetic acid. The reds, as a rule, are affected by acids, and, therefore, it is not possible to use an acid bath with Benzopurpurine, Congo red, with the possible exception of the Titan reds and scarlets, Diamine scarlet, Benzo fast scarlet, Purpuramine, which are faster to acetic acid than the other reds of this class of dye-stuffs.
Probably the best plan of dyeing these colours is to first heat the bath to about 160° F., then enter the goods, and turn over two or three times to ensure that they are thoroughly impregnated with dye-liquor. The bath is now raised to the boil, and, steam being turned off, the goods are handled without further steam until the desired shade is obtained. Another plan is to enter the goods when the bath is at about 150° F., and, after raising to the boil, to work for half to one hour at that heat; but the plan first described gives rather better results, and is far preferable. The dye-baths, as a rule, are not completely exhausted, except when very pale shades are being dyed; in no case is it necessary to throw the dye-bath away, but simply to add the required amount of dye-stuff for anew batch; with those colouring matters which are not entirely exhausted from the bath a smaller amount, generally about three-fourths only, is required to be added, with about one-third the quantity of salt which was added to the first bath. Of course it is not advisable to keep the same bath or liquor in work always, but after about twenty or thirty batches of goods are dyed to throw it away and start a fresh liquor.
As a rule it will be found that these dye-stuffs are more thoroughly taken up from the bath than is the case in dyeing cotton; thus often with the same amount of dye-stuff in proportion to the material used the wool will dye rather a deeper shade than will cotton. In some cases, especially with the blues and violets, the shade is greatly different on wool from what it is on cotton, being generally redder and much stronger. (See the chapter on Union Dyeing.) While the shades are somewhat faster to light on wool than they are on cotton, they are no faster to soaping and in some cases not so fast. What may be the function of the salt, or other such added substance, is not very clear, probably it plays the same part as to similar bodies in dyeing the basic dye-stuffs. The dye-stuffs which are referred to above are all derived from coal-tar, and in the recipes which follow many examples of their use will be found.
There are but few natural dye-stuffs that have any direct affinity for wool. Turmeric, saffron, anotta, are about the only representatives, and these are not of much importance in wool dyeing by themselves, although they are sometimes used in conjunction with other natural dye-stuffs, when they are applied by a process which is adapted more especially for the other dye-stuff which is used.
Second Method.--The method of wool dyeing now being dealt with does not differ essentially from that described above, but as it is applied to quite a different class of dye-stuffs it is thought better to consider it as a second method. Thedye-stuffs made use of in this method are what are called the basic coal-tar colours, and it may be remarked in passing that there are no natural colouring matters having the same properties. These dye-stuffs are derived from a number of so-called colour bases, such as Rosaniline, Pararosaniline, Methylrosaniline, Phenyl-rosaniline, and Auramine base. Many of these are colourless bodies containing the Amidogen group NH2, which imparts to them basic properties enabling them to combine with solids to form salts, and these salts have a strong colouring power. They form the commercial dye-stuffs Magenta, Saffranine, Thioflavine T, Auramine, Benzoflavine, Brilliant green, Methyl violet, etc., and these are salts (usually the hydrochloride) of colour bases. All these basic dye-stuffs have strong affinity for the wool fibre, and will immediately combine with it, dyeing it in colours which resist washing, etc., to a considerable extent, although there are great differences between the various members of the group in this respect. It has been shown that what takes place in dying wool with these colouring matters is that the colour base combines with the fibre the acid of the dye-stuff remaining in the dye-liquor.
Although it is possible to dye wool with the basic dyes from a plain bath containing water only, yet the results are not satisfactory, especially when working on a large scale; and for dyeing pale shades especially, the affinity of the dye-stuff for the fibre is so great that the first portions of the goods which are entered into the dye-bath have a great tendency to absorb all the dye-stuff, or the larger proportion of it, so that uneven dyeing is the result, one end of the piece of cloth being darker than the other end. This defect is particularly accentuated when pale tints are being dyed, the colouring matter being completely absorbed before all the goods are entered into the bath, but it may be remedied by adding the dye-stuff to the bath in small quantities at intervals during theprocess of dyeing. The best and most satisfactory method, however, is to add to the bath 10 per cent. of the weight of the wool of Glauber's salt, or some other neutral alkaline salt, which addition almost entirely prevents any defect of uneven dyeing. How these assistant mordants act is somewhat uncertain, the explanation generally given is that they exert a slightly solvent action on the dye-stuff, and so prevent it from going upon the fibre too readily. This is scarcely an adequate explanation, but in want of a better it will have to stand.
The affinity of the basic dyes for wool increases with increase of temperature. This is a property that has an important bearing on the method of dyeing, and to any person who pays some attention to theory in its practical applications it indicates the most rational method of working, which is to enter the goods into the bath cold, or, at the most, at a hand heat, then, after working a short time to get the goods thoroughly impregnated with the dye-stuff, to gradually raise the temperature to the boil and work for from half an hour to an hour longer, even if before this time the dye-bath be exhausted. The reason for giving a fair length of time in the bath is to get the colour properly fixed on the fibre. The combination of the dye-stuff and the fibre is a chemical one, and, as stated above, the dye-stuff has to be decomposed so that the base may combine with the essential constituent of the wool fibre, while it is obvious that this decomposition and then the union of the colour base with the wool must take time, and as it is effected more easily and completely at the boiling point, it is advisable to work the goods in the bath so as to fully insure that they are given the necessary time for the chemical change to take place.
The dye-bath is generally completely exhausted of colour, but if fairly clean it need not be thrown away, but used for another batch of wool by simply adding more Glauber's salt anddye-stuff. After a time the bath gets too dirty to used, when it may be thrown away, and a new dye-liquor made up.
In dyeing for pale shades it is best to add the dye-stuff in small quantities at intervals during the process of dyeing, and to run the goods quickly through the bath, so as not to give the dye-stuff too much opportunity to become absorbed by a portion of the goods only.
Working according to the hints given above, the dyeing of wool with the basic coal-tar colours may be carried out in a very satisfactory manner.
Third Method.--This method consists in dyeing the wool in a bath containing the dye-stuff, a little acid (usually sulphuric) with the addition of Glauber's salt, or some other alkaline salt, the essential feature or principle being that the bath is an acid one. This method is applicable to the large group of azo dye-stuffs derived from coal tar, and also to the acid dyes prepared from the basic coal-tar colours by the process of sulphonation.
It is also used to apply indigo carmine to wool, probably the only good example of a natural dye-stuff applied by this process. Most of the natural colouring matters, such as logwood and fustic, belong to another group of dye-stuffs.
The simple azo dyes are combinations of two or more organic bases, united together by a peculiar and characteristic group of nitrogen atoms. Such azo colours are, however, insoluble in water, and therefore they cannot be used in dyeing and textile colouring, although the firm of Messrs. Read Holliday & Sons years ago patented a process whereby these insoluble azo colours could be developed on the cotton fibre direct, and thus fabrics made from that fibre could be dyed in fast colours. When these insoluble azo colours are treated with sulphuric acid they are converted into sulpho acids, undergoing what is called sulphonation, an operation of the greatestimportance and value in the preparation of dye-stuffs. The preparation of indigo extract or indigo carmine from indigo is also a case of sulphonation. The sulpho-acids of the azo colours, of the basic dyes, and of indigo are usually insoluble in water, although there are great differences in their properties in this respect. They will combine with bases such as soda, calcium and potash to form salts which are soluble in water, and it is usually in the form of sodium salts that these azo and acid dye-stuffs are sold to the dyer and calico printer. It is this power of combination with bases that makes them of value in wool dyeing. As Knecht and other authorities have pointed out, the wool fibre contains a basic principle capable of combining with acid bodies, and in wool dyeing with the colouring matters under discussion, this combination occurs between the sulpho-acid of the dye-stuff and the basic principle of the wool fibre.
This points to the fact that the dye-stuffs of this class do not combine with the wool in the form in which they are supplied to the dyer as sodium salts, which is shown by a property that many if not all of them possess, of not dyeing the wool fibre in a neutral bath. If a piece of wool be immersed in a solution of, say, a scarlet or indigo extract, which is neutral it is not dyed. The dye-liquor may penetrate thoroughly throughout the fabric, but if the piece of wool be lifted out, and allowed to drain, nearly all the liquor will drain away, and leave the wool nearly if not quite white, showing that the dye-stuff in the form in which it is sold has no affinity for the wool fibre. If now a few drops of sulphuric acid be added to the dye-liquor the wool will become dyed. The sulphuric acid liberates the free sulpho-acid of the dye-stuff, and this is now in a form to combine with the wool fibre, which it does. This is the fundamental principle underlying the acid method for dyeing wool with the acid group of colouring matters.
Thepractical application of the principle laid down above is a matter of simplicity compared with the other methods of dyeing. The composition of the bath is given above. It is best to enter the wool at from 150° to 160° F. and then to raise the temperature slowly to the boil. This method of proceeding gives time for the free colour acid of the dye to be liberated from the dye-stuff on the one hand, and for its combination with the wool fibre on the other. In dyeing pale tints with acid dye-stuffs it is a good plan not to add the acid until after the goods have been entered into the bath and worked for a short time to enable them to become impregnated with the dye-liquor; the acid may be then added, and the dyeing may be finished as usual.
By this plan of working more even dyeings can be obtained than by simply entering the goods direct into an acidified dye-liquor.
Any kind of acid may be employed, but generally sulphuric acid is used, partly because it is cheap, and partly because it is the commonest acid known. Acetic acid is also used in many cases.
Fourth Method.--We now come to the fourth method of dyeing wool. Strictly, perhaps, it is not a single method, but a group of methods, which are used to supply a certain class of dye-stuffs to the wool fibre; but as the governing principle depends upon the peculiar property of the dye-stuffs now to be noticed, which underlies all the variations of the process of dyeing, it has been thought better to speak of the fourth method rather than to subdivide further, in which case the fundamental principle might be lost sight of.
The class of dye-stuffs included in the fourth group was named by Bancroft the "adjective" group, because they require the aid of a second body, named the mordant, to properly develop and to fix the colour of the dye-stuff on the wool. It is sometimes known as the "mordant dye-stuff" class,and this is perhaps its best name. This group of colouring matters comprises dye-stuffs of both natural and artificial origin, the latter of which are getting very numerous and valuable, and bid fair to displace the natural members of the group. With but few exceptions the adjective dye-stuffs are not colouring matters of themselves,i.e., they will not dye wool or other fibres by themselves. Some are coloured bodies, such as fustic, logwood, Persian berries, Anthracene yellow, etc., but many are not so, and some possess but little colour, which, moreover, gives no clue to the colours that can be developed therefrom.
All the colouring matters of this class possess either a distinctively acid character, or belong to the class of phenols, which, while not being true acids, still possess weak acid functions that enable them to combine with bases like acids. These bodies have the property of combining with bases and metallic oxides, such as soda, potash, iron, alumina, chrome, tin, nickel, cobalt, etc., forming a series of salts. Those of soda and potash are usually soluble in water, while those of the other metals are insoluble, and are usually of strong colour. It is on this property of forming these insoluble coloured bodies, colour lakes, as they are called, that the value of the adjective dye-stuffs in dyeing depends.
The group of adjective colouring matters may be subdivided into two divisions, not depending upon any differences in the mode of application, but upon certain differences in the results they give. Perhaps the best example of an adjective dye-stuff is Alizarine. This body has a faint red colour, but of itself possesses absolutely no colouring power. When, however, it is brought into combination with such metallic oxide as alumina, iron and chrome, then it forms coloured bodies, the colour of which varies with the metal with which it is in union, thus with alumina, it is a bright red; with iron, a dark violet, almost black; with chrome, adeep red; with tin, a scarlet; and so on. This is a representative of the true adjective dyes, which comprise most of the so-called Alizarine dye-stuffs, and logwood, fustic, and most of the natural dye-stuffs. Another division of the group includes a few colouring matters of recent introduction, like Azo green, Alizarine yellow, Galloflavine, Anthracene yellow, Flavazol, etc., which, while forming insoluble colour lakes with metallic oxides, do not give different colours with different metals.
This class of dye-stuffs, owing to their forming these insoluble colours, gives really fast colours, capable of resisting lengthened exposure to light and air, and resisting washing, acids and alkalies. Of course there are differences between the various members of the group in this respect, and even the resisting power of an individual member depends a good deal on the metal with which it is combined, and the care with which the process of dyeing has been carried out.
In the dyeing of these adjective dye-stuffs, upon the various fibres, and on wool in any particular, the object is to bring about in any convenient way the formation on the fibre of the metallic combination of the colouring principle and the mordant, and it is obvious that if a satisfactory result is to be obtained, then this must be done in a very thorough manner. There are three ways in which this combination of colouring principle and mordant may be brought about in dyeing wool with these bodies, we may either mordant the wool first, and then apply the dye-stuff, or we may impregnate the wool with the dye-stuff first, and then fix or develop the colour afterwards, or, lastly, we may carry on both operations in one process. Each of these methods will now be discussed, and their relative advantages pointed out.
The mordanting method is one of the most generally useful. It consists in first causing a combination of the metalwith the wool fibre. This is carried out by boiling the wool in a solution of the metal, such as bichromate of potash, chrome alum or chrome fluoride when chrome is to be used as a mordant, with alum or sulphate of alumina when alumina is required to be deposited on the fibre, and with copperas when iron is to be the mordant. It is best to add a little oxalic acid, cream of tartar, or tartaric acid to the mordanting bath, which addition helps in the decomposition of the metallic salt by the wool fibre, and the deposition of the metallic oxide on the wool. With bichromate of potash, sulphuric acid is often used, much depending upon the character of the mordant required. Some dye-stuffs, such as logwood for blacks, work best when the wool is mordanted with chromic acid, which is effected when sulphuric acid is the assistant mordant. Other dye-stuffs, such as fustic, Persian berries and Alizarine yellow, are best dyed on a basic chrome mordant, which is effected when tartar or oxalic acid is the assistant mordant used, or when some other form of chrome compound than bichrome is employed.
The actual mordanting is done by boiling the wool in a bath of the mordant, the quantity of which should be varied according to the particular mordant that is being employed and to the quantity of dye-stuffs which is to be used. It is obvious that for a fixing deep shade of, say, Alizarine on the wool, a larger quantity of mordant will be required than to fix a pale shade; sometimes this point is overlooked and the same amount of mordant employed for pale or deep shades. The best plan of carrying out the mordanting is to enter the wool in the cold bath or at a hand heat, and then raise to the boil and continue the boiling for one hour; of course the goods should be kept turned over during the process to facilitate the even mordanting of the wool. A great deal of the success of dyeing with the dye-stuffs now under consideration dependsupon the efficiency with which the mordanting has been carried out. If this is at all unevenly done then no amount of care in the succeeding dyeing process will lead to the development of an even dyeing. After the mordanting is finished the goods should be rinsed with water, but it is not necessary to dry them.
The next stage in the process is the actual dyeing operations, which is done by immersing the mordanted wool in a bath of the dye-stuff or mixture of dye-stuffs.
The fundamental principle is to bring about the combination between the colouring principle of the dye-stuff and the metallic oxide which has been deposited on the wool in the previous mordanting process. As neither of these bodies, however, is very energetic it follows that the action must be a slow one, and, therefore, time is a highly important factor in the dyeing of wool by the mordanting process. The combination between the dye-stuff and the mordant is influenced also by temperature, and is most active at the boiling point of water. It is, therefore, needful to conduct this operation at that temperature, but it would be a wrong way to introduce the mordanted material into a boiling bath of the dye-stuff; nothing would conduce to uneven dyeing so much as that course. The best method of working, which, moreover, is most particularly applicable to the series of Alizarine dye-stuffs, is to enter the goods in a cold bath of the dye-stuff, and to work them for a short time to get them thoroughly impregnated, a condition which is essential if even dyeing is the goal aimed at, then to raise the temperature of the bath gradually to the boil, the goods being in the meantime well worked. The dyeing is continued for from one to one and a half hours at the boil.
It is important in dyeing by this process, especially when using Alizarine, to keep the temperature of the bath as uniform as possible, and the goods well worked. Alizarine, and someother members of this class, are rather sensitive to heat, and if a dye-vat be hot at the bottom and cold at the top uneven dyeing is sure to be the result; this is due to the greater affinity of the Alizarine for the mordant at the high than at the low temperature, and thus more is fixed on to the wool. The remedy for this is to so construct the heating arrangements of the vat that the temperature shall be as uniform as possible, while the goods should be kept continually turned over, and every portion of them brought into intimate contact with the dye-liquor. The continuance of the dyeing operations for one and a half to two hours after the vat has reached the boil is necessary to properly develop and fix the colour on the fibre; a short boil leaves the goods of a poor shade, without any solidity about it, and the colour is loose, while a longer boil brings up a solid shade and a fast colour.
Although it is not absolutely necessary to add any acid to the dye-bath during the dyeing operations, yet as the Alizarines and most of this class of dye-stuffs dye better in a slightly acid bath it is advisable to add a small quantity of acetic acid, say about one pint to every 100 lb. of goods; this serves to correct any alkalinity of the water, which may be due to its containing any lime. Dye-stuffs of the acid class, such as indigo extract, Cloth red, Acid magenta, etc., may be used along with the Alizarine dye-stuffs, in which case the addition of acid to the dye-bath becomes necessary, but too great an excess of acid should be avoided, as it interferes somewhat with the dyeing of the mordant dyes.
This is by far the best and most generally used method of applying these mordant dyes. It is not a costly process, being indeed economical, as it only requires just the right amounts of drugs and dye-stuffs, and there is the minimum loss of material in the mordanting and dye-baths. Shades can be brought up with the greatest ease, although it is well inthe dyeing to add rather less dye-stuff than is actually required, and to add more when it is seen how the shade is coming up. The labour is the most important item in the mordanting and dyeing method.
The proportions of material used to the weight of the wool are: Of bichromate of potash, 3 per cent. for full shades, and 1 per cent. for pale shades; of fluoride of chrome, the same quantities; of acetate of chrome, according to the strength of the solution used; of alum, 10 to 20 per cent.; of sulphate of alumina, 5 to 10 per cent.; of copperas, 5 to 10 per cent.; of tartar, 1-1/2 to 2-1/2 per cent.; of oxalic acid, 1 to 1-1/2 per cent.; of sulphuric acid, 1 per cent.; of argol, 2-1/2 to 5 per cent.; of tartaric acid, 1 to 1-1/2 per cent.; but of course in an article like this it is impossible to give definite quantities.
Second Method.Stuffing and Saddening.--This method consists in first treating the wool with a solution of the dye-stuff, and then with a solution of the mordant required to develop and fix the colour. This method is more particularly applicable to such dye-stuffs as camwood, cutch, logwood, madder, fustic, etc., the colouring principles of which have some affinity for the wool fibre and will directly combine with it. It is not suitable for the application of the Alizarine colours. The saddening may be and is commonly done in the same bath, that is, after the wool has been stuffed it is lifted, the mordant--copperas, bluestone, bichrome, or alum--is added, and the wool is re-entered into the bath. This cannot be considered a good method of working; the shades obtained are full and deep and fairly fast, but there is usually a considerable loss of colouring matter, as the wool in no case abstracts the whole of the dye-stuff from the bath; what excess is left combines with the mordant when the latter is added, forming an insoluble colour lake, which falls down to the bottom of the dye-vat and is wasted, or it may go upon thewool in a loose, unfixed form, and cause it to rub badly and come off in milling. Then it is rather difficult to dye to shade, much of the result depending on conditions over which the dyer has little control. Working as he does with dye-stuffs of unknown colouring power, which may vary from time to time with every fresh batch of material, it is evident that, although the same quantities may be used at all times, at one time a deeper shade may be obtained than at another, and as it is impossible to see what is going to be the result, and if by mischance the shade does not come deep enough it cannot well be rectified by adding a quantity of dye-wood to the bath, because the mordant in the latter will prevent the colouring matter from being properly extracted, and only a part of that which is extracted is fixed on the wool, the rest being thrown away in the dye-bath, and partly on the particles of wood themselves, when logwood, camwood, etc., are used in the form of chips or powder. Dyers being well aware of this, are in the habit when mistakes occur of bringing up to shade with soluble dye-stuffs--archil, indigo extract, and such like.
This method, as stated above, is very wasteful, not only of dye-stuffs, but of mordants. In no case does the wool absorb the whole of the colouring matter from the bath, the unabsorbed portion goes down to the bottom of the bath when the mordant is added, so that when the dyeing is finished, the dye-bath is charged with a large quantity of colouring matter in an unusable form which has to be thrown away, thus at once adding to the pollution of the river into which it is run, and to the cost of the process of dyeing. As attention is being directed more and more to the question of the prevention of pollution of rivers, and as the waste liquors from dye-works add to the apparent pollution to a very considerable extent, dyers will have to develop other modes of dyeing than that of stuffing and saddening in one bath.
Theprinciple of dyeing by stuffing and saddening may be carried out by the use of two separate baths; in fact, it is done in the case of dyeing a cutch brown from cutch and bichromate of potash. The goods are first treated in a bath of the dye-wood for a short time, then rinsed, and the colour is developed by padding into a saddening bath of the mordant. By this method the baths, which are never quite exhausted, can be retained for future use, only requiring about 1/2 to 3/4 of the original quantities to be added for each succeeding batch of the goods, in fact, in some cases, as in cutch, old baths work better than new ones.
The advantage attached to this method of working is that arising from economy of dye-stuff and mordant, and the reduction of the pollution of the stream on which the works are situated. The disadvantages are that the cost of labour is increased by there being two baths instead of one, and that the shades obtained are not always so full as with the one-bath method. This, of course, can be remedied by running the goods through the baths again, which, however, adds to the cost of the process, but there is this much to be said, the shade can be better brought up than by the one-bath process. In some cases the methods of mordanting, dyeing and saddening are combined together in the dyeing of wool, thus, for instance, a brown can be dyed by first mordanting with bichrome, then dyeing with camwood and saddening in the same bath with copperas. The shades obtained are fairly fast and will stand milling. The disadvantages of this process are the same as those attached to the dyeing and saddening in one bath.
Now we come to the last method of dyeing wool with mordant and colours, that in which the operation is carried out in one bath. This can only be done in those cases where the colour lake that is formed is somewhat soluble in dye-liquors, which usually have slightly acid properties; orwhere the affinity between the two bodies (colouring matter and mordant) is too great. This method can be carried out in, for instance, dyeing a cochineal scarlet with tin crystals, a yellow from fustic and alum, a black from logwood and copperas and bluestone, a red from madder and bichrome, and the dyeing of the Alizarine colours by the use of chrome fluoride, etc.
The shades obtained are usually not so deep as those got by the mordanting and dyeing process, but are frequently nearly so. In some cases, as in dyeing with fustic or logwood, it gives rather brighter colours, due to the fact that the tanning matters present in the dye-stuffs is not fixed on the wool, as is the case with the mordanting method, but is retained in the dye-bath. For dyeing with logwood and copperas or bluestone the process is not a good one, as it does not give as full shades as by the ordinary process. For dyeing with the Alizarine colours, using chrome fluoride as the mordant, it can be applied with fair success. There are advantages in the saving of time and labour and in the amount of steam required, all of which are important items in dyeing.
It is rather troublesome to match off by this process, but it can be done. For light shades the process will be found very useful, as these cost less than by any other process. The dye-baths may be retained for future use, although in process of time they become too dirty for use, when they must be thrown away.
Level Dyeing.--The first condition for successful dyeing is that the fibres to be treated are absolutely clean. A careful washing is not enough for this purpose. Cleanliness is undoubtedly the condition which the fibre must possess to enable the dye to hold on and not to come off the fibre, this latter causes a loss of dye-stuff, soils the whites, and gives rise to trouble between the dyer and finisher; it is alsothe condition for making the dye go on the wool evenly. The washing must be done at the boil, so that the fibre is well wetted out and all the air bubbles adhering to it are driven out. But this is not enough; it must be accompanied by a scouring operation, not only in the case of fibres of which the dyer does not know whether they have been scoured, but also when they have already been scoured and bleached. The kind of scouring that the fibres receive in this case need only be of a comparatively light character, but it must never be omitted, even for dark shades, as the traces of grease which the fibre contains are the causes of nearly irremediable stains in the dyeing operations. Even in dyeing black wool it is of the greatest importance to have the fibre suitably scoured.
The fatty matters which the fibre contains may belong to the components of the fibre itself and be natural matters, but in the case of wool yarns and cloths they are mostly dressing oils, from which the dyer cannot be too anxious to free the wool before dyeing. Some practical methods of preparatory treatment of the fibres before dyeing may therefore be described here with advantage.
Cotton is boiled off at actual boiling heat for two hours, with 8 per cent. of its weight of carbonate of soda and a little soft soap, which treatment is sufficient for dark colours.
For light colours it is necessary that the cotton be bleached. Wool is scoured with soda and soap in the proportion of 10 lb. soda and 2 lb. Marseilles soap for 100 lb. wool. Silk is scoured by boiling for one and a half hours in a boiling bath with 30 per cent. of its weight of soap. For light colours a second boiling should be given, with 15 per cent.
The careful cleaning of wool previous to dyeing is of exceptional importance. Raw wool is cleaned with carbonate of soda and ammonia. For 50 lb. wool to be cleaned 6 lb. carbonateof soda and 1-1/2 lb. ammonia are added to a bath of 150 gallons water. The wool is laid down in it for twenty minutes at 35° C., taken up, squeezed, treated for fifteen minutes in another bath, with 5 lb. carbonate of soda and then rinsed. The first bath must be renewed as often as possible, because it contains all the impurities. In the case of woollen yarn 30 lb. require two tubs of 40 gallons capacity. The first tub is to contain 35 gallons water and 2 lb. ammonia at 10° Be. After working the skeins for three minutes in it they are left to stand for fifteen minutes, then wrung out, and the operation is repeated in the second tub. Finally, the yarn is rinsed several times in soft water.
Woollen piece goods are treated in a large wooden tub at 40° C. with 4 lb. carbonate of soda and 2 lb. carbonate of ammonia for 80 lb. material. The pieces are moved about for twenty minutes, laid down in the bath overnight, again turned for ten minutes and hydro-extracted. They may also be handled for forty minutes in a bath of 2 oz. ammonia for 100 lb. wool at 60° C., and then for twenty minutes in clear water at 60° C.
After wetting or preparatory treatment, it will be best to proceed immediately to dyeing; if the fibres be left in a heap for too long a time, there is danger that they may become heated, or at least that the moisture may be irregularly distributed by the occurrence of partial drying, causing an uneven fixation of the colour in the first stages of dyeing. The first two conditions of successful dyeing are, therefore, a suitable wetting out and scouring. The dyer, however, must not be less careful to see that the dye-bath is what it ought to be.
Whenever possible the dye-stuff must be dissolved separately, or at least the bath not entered before the dye-stuff is well dissolved. Artificial dye-stuffs require particular attention to this point, because the presence of undissolved particlesis the cause of irregularities, such as streaks, or, at least, specks. The solution is mostly made hot as follows: After pouring water at 180° F. upon the dye-stuff, stir gently, strain through flannel or through a very fine sieve, and pour more water upon the residue until nothing more is dissolved. As is well known, the artificial dye-stuffs often contain insoluble matter, resins, etc. It is therefore advisable to use only soft water for this operation.
The solutions of artificial dye-stuffs are ordinarily made at the rate of 1 to 5 lb. per 10 gallons of water, 2 lb. being the proportion mostly employed. This depends more or less on the solubility of the dye-stuff. Old solutions sometimes contain crystals of the dye-stuff which have separated out. These should be redissolved by heating before the solution is used. But it is best to make only such a quantity of solution as will suffice for immediate requirements.
With paste colours care should be taken to keep them in closed vessels in such a manner that they will not become hard by evaporation, and they should not be kept in any place where they are likely to freeze in winter time. In such an event it is not an uncommon circumstance for the casks or other vessels containing them to burst, with a consequent loss of dye-stuff. Before any of the paste is withdrawn from the cask, it is advisable to stir well up with a wooden stirrer.
In adding dye-stuff during the actual dyeing operation, it is advisable to add the dye-stuff to the bath in two or three portions, always taking out the goods before adding each lot of dye-stuff, and stirring up the contents of the bath before re-entering the goods. Another important condition of obtaining a level dyeing is to proceed slowly, beginning with a weak bath at a moderate temperature, and rising gradually to a boil. If necessary to retard the dyeing from the commencement, then an assistant mordant is added to the dye-bath, in the shape of soda crystals or phosphate of soda for thebenzidine colours on cotton; bisulphate of soda or Glauber's salt in dyeing with azo colours or acid colours on wool; or tartar may be used in most cases with good effect, causing the wool to have a softer feel. Finally, the evenness of the dyeing is much increased by the frequent turning over of the material in the dye-bath, so managing this in the case of wool as to avoid felting.
When dyeing with a mordant, the dyer should see that the mordanting operation is thoroughly well done, for as much care is required for the mordanting as for the actual dyeing; in fact, if anything, the mordanting should be done with rather more care, as if it be at all defective no amount of care in the following dyeing operations will ensure a level dyeing. Chrome mordanted wool should be dyed without delay, as it is rather sensitive to light, especially the yellow sort, which gradually changes into the green sort of chromed wool.
One peculiarity of dyed wool is that it will continue to take up colour after it is removed from the dye-bath, especially if it contains any of the hot dye-liquor, therefore it is very desirable to wash the wool as soon as possible after its removal from the dye-bath. It is best, however, not to take the wool out of the hot bath, but to leave it in until the bath becomes cool, and then to take it out, by this means the colour becomes deeper and more solid looking, and is faster on the wool.
One cause of irregular dyeing may be mentioned, as it is occasionally met with, namely, the presence of foreign fibres in the goods, cotton in wool fabrics, and even of different varieties of the same fibre. All dyers know that dead or immature cotton will not dye up properly, a fact or defect more especially met with in indigo dyeing than probably in any other colour. Then wools from different breeds of sheep vary considerably in their dyeing power. Fine wools take upmore colour than coarse, and, consequently, even from the same bath, will come out a deeper shade; if a fabric, therefore, contains the two kinds of cotton, or the two kinds of wool, they will not dye up evenly.
In the preceding sections brief notes have been given about the principal methods of dyeing wool, with some indications of the dyes which can be used under each method. In the succeeding sections will be given a number of recipes showing how, and with what dye-stuffs, various colours, shades and tints can be dyed upon wool. It will be understood that these recipes are applicable to all kinds of woollen fabrics, loose wool, slubbing, yarns in any form, woven worsted or woollen cloths, felts of any kind, etc., all these different forms require handling in a different way; it would not do, for instance, to treat a quantity of slubbing in the same way as a piece of worsted cloth, while hanks of yarn require a different mode of handling to a quantity of hat bodies. The different kinds of woollen fabrics require to be dealt with in different kinds of machines, and this has already been dealt with in the chapter on Dyeing Machinery and Dyeing Manipulations.
To describe and illustrate the application of all the various woollen dye-stuffs, whether of natural or artificial origin, and to show the great variety of shades, etc., which can be obtained with them, either all one or in combination, would require not one, but many volumes of the size that this present work is intended to be. Therefore, it becomes necessary to make a selection from the best-known and most used of the various dyes, and illustrate their application by a number of recipes, all of which, unless otherwise stated, are intended to be for 100 lb. weight of woollen material of any kind. It may also be pointed out that, as a rule, the recipes may be applied to the dyeing of fabrics made with other animal fibres than the wool of the sheep, as, foralpaca, cashmere, camel-hair, hare or rabbit fur, etc., inasmuch, as, with the exception of silk, all animal fibres practically possess the same dyeing properties.
It will be convenient to point out here that a very large proportion of the shades dyed on wool and other fabrics are obtained, not by the use of a single dye-stuff, although this should always be done, whenever possible, but by the combination of two or more dye-stuffs together in various proportions. It is truly astonishing what a great range of shades can thus be dyed by using two or three dyes suitably mixed together, and one of the things which go to making a successful dyer and colourist is the grasping of this fact by careful observation, and working accordingly. Dyers will find much assistance in acquiring a knowledge of colour and colour mixing from the two little books onColour, by Mr. George H. Hurst, and theScience of Colour Mixing, by Mr. David Paterson, both issued by Messrs. Scott, Greenwood & Co., the publishers of the present work.
Black on Wool.--Until within a comparatively recent time black was dyed on wool solely by the use of logwood, combined with a few other natural dye-stuffs, such as fustic, indigo, etc., but of late the researches of colour chemists have resulted in the production of a large number of black dyes obtained from various coal-tar products. These have come largely into use, but still, so far they have not been able to entirely displace logwood, chiefly on the score of greater cost, the use of the natural dye still remaining the cheapest way of producing a black on wool; although the blacks yielded by some of the coal-tar black dyes are superior to it in point of intensity of colour and fastness to scouring, acids and light, as well as being easier to dye.
Blacks may be obtained from logwood by several methods, either by previous mordanting of the wool or by the stuffing and saddening methods, or by the one-bath process. The followingrecipes will show how these various methods are carried out in practice:--
Chrome Logwood Black.--The wool is first mordanted by boiling for one and a half hours with 3 lb. bichromate of potash and 1 lb. of sulphuric acid, working well the whole of the time. It is not advisable to exceed the amounts of either the bichromate or the acid here given, these quantities will result in a full bloomy black being obtained, but any excess gives rise to greyish dull blacks, which are undesirable. After mordanting rinse well with water, when the goods will be quite ready for the dye-bath.
The dyeing is done in a bath made from a decoction of 40 lb. of good logwood. It is perhaps preferable to start cold or only lukewarm, raise to the boil and work for one hour, then lift, rinse well, and pass into a boiling bath made from 1 lb. of bichromate of potash and 1/4 lb. of sulphuric acid for half an hour. This extra chrome bath fixes any colouring matter which may have been absorbed by the wool but not properly fixed by the mordant already on, it leads to fuller shades which are faster to rubbing and milling.
The mordanting bath may be kept standing and used again for fresh lots of wool, in which case it is only necessary to add 2-1/2 lb. of bichromate of potash and 1 lb. sulphuric acid to the bath for each additional lot of wool that is being dealt with. Old mordant baths work rather better than new ones, but the use cannot be prolonged indefinitely, there comes a time when the bath gets too dirty to use and then it must be thrown away.
During the operation the bichromate of potash becomes more or less decomposed and there is formed on the wool fibre a deposit of chromic acid and chromic oxide, this deposit forms the mordant that in the subsequent dye-bath combines with and fixes the colouring matter, the hæmatoxylin of the logwood, and develops the black on the wool.
Inplace of sulphuric acid, hydrochloric acid can be used with some advantage as regards the proportion of bichromate decomposed, and therefore an increase in the amount of chromium oxide deposited on the wool.
This gives a deep blue black, somewhat wanting in bloom. The following recipe gives a much bloomier black, but is rather more expensive to dye.
Chrome Logwood Black.--Mordant by boiling in a bath containing 3 lb. bichromate of potash and 7 lb. tartar. Dye and otherwise treat as in the last recipe; 4 lb. of tartaric acid used in place of the tartar, gives rather brighter and bloomier shades. The use of so-called tartar substitutes is not to be recommended, they give no better results than does sulphuric acid and are much dearer to use.
A somewhat greener shade of black than is yielded by either of the above two recipes is the following:--
Chrome Logwood Black.--Mordant the wool in a bath containing 4 lb. oxalic acid and 3 lb. bichromate of potash, afterwards dyeing as in the first recipe.
All the above recipes give blacks of a bluish tone, which on the whole have a good bloomy and solid appearance. Often what is called a jet black is wanted, this can be obtained by following the recipe given below.
Chrome Logwood Jet Black.--Mordant the wool by any of the methods given above. The dyeing is done in a bath made from 40 lb. logwood and 5 lb. fustic, working as described in the first recipe. Using these properties a good jet black is obtained, which is quite satisfactory on the score of solidity and fastness. It is not advisable to exceed the quantity of fustic here given, or otherwise the black will have a tendency to assume a greenish tone that is not at all desirable. This greening becomes more marked when from 7-1/2 to 10 lb. of fustic is used, or if alum be added to the mordant along with the bichromate of potash.
Chromeblacks are the best blacks which can be obtained from logwood. They have, however, a tendency to turn green on exposure to the weather, which tendency seems to be most prevalent in those blacks in which sulphuric acid has been used as the acid constituent of the mordanting bath. The greening may be reduced to a minimum by adding to the dye-bath about 1 to 2 lb. of Alizarine. Another plan which has been followed is to give the wool a bottom with 5 to 6 lb. of camwood or peachwood, then mordanting and dyeing us usual.
Logwood Black on Wool.--Boil first for one hour with a decoction of 8 lb. camwood, then lay down for fifty minutes in a boiling bath of 3 lb. bichromate of potash, 1 lb. alum, 1 lb. tartar. It is a good plan to allow the goods to hang overnight.
The dye-bath is prepared with 45 lb. logwood, 8 lb. fustic, 4 lb. sumac. Dye one hour at the boil, wash and dry.
Indigo Black.--This is sometimes called woaded black, and has an excellent reputation as a fast black. It is dyed by first giving the wool a medium blue bottom in the indigo vat by the method of vat dyeing, which will be described later on, and then dyeing by either the second or third recipe given above. The use of sulphuric acid is rather to be avoided in dyeing an indigo vat with chrome and logwood, as the chromic acid set free during the process is likely to attack and by destroying the indigo to materially reduce the intensity of the blue bottom. Or, after blueing in the vat, the black may be dyed or topped on by the process with copperas, which will be described below.
Iron Logwood Black.--Mordant the wool by boiling one and a half to two hours in a bath made with 5 lb. copperas, 2 lb. bluestone, 2 lb. alum, and 10 lb. argol. The dyeing is done in a bath of 50 lb. logwood.
It is not advisable to use more argol than is here given, foralthough a little excess will not materially affect the beauty or brilliancy of the resulting shade, yet such excess is wasteful, and makes the dyeing cost more than it otherwise would. On the other hand, too little will cause the shade to become greyish in tone and wanting in solidity. The copper sulphate (bluestone) added increases the fastness of the finished black to light, the best proportions to add are from 2 lb. to 4 lb. for 100 lb. of wool. The shade obtained in the above recipe is of a bluish-violet hue, if a jet black be wanted, add 5 lb. of fustic to the dye-bath. Another and very common method of working is the "stuffing and saddening" process, given in the next recipe.
Iron Logwood Black.--Make a bath of 50 lb. logwood, 6 lb. fustic, and 1 lb. sumac. Work the wool in this for one hour at the boil, lift, allow the bath to become cool, then add 6 lb. of copperas (ferrous sulphate) and 2 lb. bluestone; re-enter the wool, raise the temperature to the boil, and work half an hour, then lift, wash and dry. On the whole the first method is the most economical and yields the best blacks, fastest to rubbing.
The iron-copper-logwood blacks are not so fast to acids as the chrome-logwood blacks, but they are rather faster to light and air, and equally so to scouring and milling.
One-bath methods of dyeing blacks are sometimes preferred by wool dyers. Of these the following is an example.
Logwood Black.--Make a dye-bath with 50 lb. logwood, 5 lb. fustic, 6 lb. copperas, 2 lb. copper sulphate, and 4 lb. oxalic acid. Enter the goods and work at the boil to shade. The oxalic acid is added for the purpose of retaining the logwood-iron-copper black lake, which is formed on mixing the various ingredients together in solution. On boiling the wool in the liquor the fibre gradually extracts out the dye matter and becomes dyed. The use of some of the so-called "directblacks" (noir reduit, Bonsor's black) is based on the same principle.
These dyes are mixtures of logwood, fustic or other dye-stuff with copperas, bluestone and oxalic acid, and only require adding to water to make the dye-bath. This method of working enables logwood to be used in conjunction with dihydroxynaphthalene and some other coal-tar derivatives to obtain blacks of good solidity and much faster to light, air, acids and scouring than the ordinary logwood blacks.
Another recipe for a one-bath logwood black, using the extracts in place of the dye-wood itself, is the following:--
Logwood Black.--Prepare a dye-bath with 12 lb. logwood extract, 2 lb. fustic extract, 6 lb. copperas, 4 lb. bluestone, 3 lb. oxalic acid, 2 lb. tartar. Boil the goods in this for one hour.
Some dyers use the dye-woods and prepare from them a decoction by boiling in water; in some respects this is the most economical plan, only the dyer has to get rid of the spent dye-wood from which the colouring matter has been extracted, and this is not always an easy matter. Some dyeing machines (Smithson's) have been devised which contain as one of their features a dye-wood extractor, in which the extraction of the colouring matter of the wood proceeds at the same time as the dyeing. Good results are got with such machines, although they leave something to be desired.
Many dyers use the dye-wood extracts which are now made on a large scale. These are for the dyer much more convenient to use, although naturally rather more costly. They are approximately five times the strength of the dye-wood, but they vary very greatly in this respect.
Logwood blacks can be readily distinguished from nearly all other blacks, in that by treatment with moderately strong hydrochloric acid they turn a bright red.
No other natural dye-stuff is used in the dyeing of black than these here given.
Oflate years many black dyes derived from coal tar have been placed on the market. Among these may be enumerated the Acid Blacks of Messrs. Bead Holliday & Sons; the Naphthol and Naphthylamine Blacks of Leopold Cassella & Co.; the Victoria Blacks of the Farbenfabriken vorm, Fr. Bayer & Co.; the Wool Blacks of the Actiengesellschaft für Anilin Fabrikation; the Azo Blacks of the Farbwerke vorm, Meister, Lucius & Bruning; and one or two other blacks. These blacks are dyed very simply, as will be seen from the recipes given below, showing their application in the production of blacks of a great variety of tone. None of them dye a true jet black, but generally a bluish black or a violet black, but the tone may be readily changed to a jet or dead black by the addition of a little orange, yellow or green dye-stuff.
They give blacks of a very solid appearance and very bright in tone, and have the advantage over the logwood blacks of leaving the wool more supple and less liable to be felted. Moreover, as a rule they are faster to acids, alkalies and milling than are the logwood blacks, and as regards fastness to light they excel that dye-stuff. Unfortunately they are more costly to use, which tells against their entirely displacing logwood in dyeing blacks on wool.
Still, year by year their use is increasing, and as their price becomes less their employment will yet further extend. They may be combined with logwood, as they will dye with equal facility on mordanted and unmordanted wool.
Violet Black on Wool.--Make the dye-bath with 4 lb. Acid Black B, or Acid Black B B, 3 lb. sulphuric acid, and 10 lb. Glauber's salt. Work at the boil for one hour. The B brand of these blacks gives shades slightly redder in tone than the B B. The blacks are quite fast to light and acids, but not to soaping.