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 haematoxylin of the logwood, and develops the black on the wool.
In place of sulphuric acid, hydrochloric acid can be used with (p. 085) 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 subst.i.tutes 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 quant.i.ty of fustic here given, or otherwise the black will have a tendency to a.s.sume 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.
Chrome blacks are the best blacks which can be obtained from (p. 086) 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 const.i.tuent 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, for (p. 087) although 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 (p. 088) "direct blacks" (_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.
Of late years many black dyes derived from coal tar have been (p. 089) placed on the market. Among these may be enumerated the Acid Blacks of Messrs. Bead Holliday & Sons; the Naphthol and Naphthylamine Blacks of Leopold Ca.s.sella & Co.; the Victoria Blacks of the Farbenfabriken vorm, Fr. Bayer & Co.; the Wool Blacks of the Actiengesellschaft fur 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.
_Blue Black on Wool_.--Dye as in the last recipe, but use Acid (p. 090) Black S. This dye-stuff produces bluer shades of black than either B or B B, and they are faster to soaping.
_Jet Black on Wool_.--Make the dye-bath with 4-1/2 lb. Acid Black S, 1/2 lb. Fast Yellow F Y, 3 lb. sulphuric acid, and 10 lb. Glauber"s salt. This shows how, by the addition of a little yellow dye-stuff, the blue shade may be changed to a full jet black.
_Blue Black on Wool_.--The dye-bath is made with 4-1/2 lb. Naphthol Black B (or 6 lb. Naphthol Black 3 B), 4 lb. sulphuric acid, and 10 lb. Glauber"s salt. Work at the boil for one hour, then lift, wash and dry. The Naphthol Blacks have long been used in wool dyeing, and give excellent results, the 3 B brand dyeing much bluer shades than the B brand. There is also a 4 R brand giving violet blacks. These blacks are quite fast to acids and alkalies, are fast to light, and resist washing very well, the B brand being the fastest. The following recipe shows how a full jet shade can be obtained for these blacks:--
_Jet Black on Wool_.--Prepare the dye-bath with 4-1/2 lb, Naphthol Black B, 1 lb. Naphthol Green B, 1/4 lb. Indian Yellow, 4 lb.
sulphuric acid, and 10 lb. Glauber"s salt.
_Blue Black on Wool_.--Make the dye-bath with 5 lb. Anthracite Black B, 10 lb. Glauber"s salt, and 5 lb. bisulphate of soda, working at the boil for one hour. Anthracite Black does not require a bath so acid as do some other coal-tar blacks. The shade obtained is a full blue black, which is fast to acids; alkalies turn it a little bluer, and soaping causes some loss of colour.
_Violet Black on Wool_.--Make the dye-bath with 5 lb. Anthracite Black R, and 10 lb. bisulphate of soda. The black thus obtained is a good one, fairly fast to acids, alkalies and soaping.
_Dead Black on Wool_.--Make the dye-bath with 6 lb. Anthracite Black R, 1 lb. Anthracene Yellow C, and 10 lb. bisulphate of soda. Work at (p. 091) the boil for one hour, then lift, add 3 lb. fluoride of chrome and work again at the boil for twenty minutes. This black is a very fine one, and is very fast.
_Violet Black on Wool_.--Make the dye-bath with 4 lb. Naphthylamine Black D, 10 lb. Glauber"s salt, and 5 lb. acetic acid. This black is pretty fast to acids, alkalies and light, but is somewhat loose to soaping, and, therefore, cannot be used for black goods that have to be strongly milled. Naphthylamine Black 4 B dyes somewhat bluer shades than the B brand.
_Blue Black on Wool_.--Prepare the dye-bath with 6 lb. Victoria Blue Black, 20 lb. Glauber"s salt, and 1-1/2 lb. acetic acid, working at the boil for one hour. A fine blue black, is obtained which is quite fast to acids, washing and light.
_Greenish Black on Wool_.--The dye-bath is made with 3 lb. Victoria Black Blue, 2 lb. Fast Yellow F Y, 20 lb. Glauber"s, salt, and 1/1-2 lb. acetic acid. The dyeing is done at the boil and takes about an hour. This shade has a good full tone, and is fast.
_Jet Black on Wool_.--Make the dye-bath with 4 lb. Victoria Black B, 1/2 lb. Fast Yellow F Y, 10 lb. Glauber"s salt, and 2 lb. sulphuric acid, working at the boil for one hour. A very fine shade is thus obtained, which is fast to acids, alkalies and soaping. By omitting the Fast Yellow a blue black is obtained, while by using Acid Green instead a greener tone is given to the black. In place of the Victoria Black B the two other brands, 5 G, and G, of these blacks may be used.
These give equally fast blacks of a deeper and more jet black.
_Black on Wool_.--Prepare a bath with 5 lb. acetic acid, 9 Tw.; enter the wool for one hour, then lift and add 5lb. Naphthol Black 3 B, and 1/4 lb. Indian Yellow. Re-enter the goods and boil for one hour, wash and dry.
Many of the black dyes--Naphthol Black, Naphthylamine Blacks, (p. 092) Naphthyl Blue Black N, Acid Black B, etc.--are capable of slowly dyeing wool from neutral baths, that is, containing only Glauber"s salt, or rather more quickly if a little acetic acid be present. Such dyes are very useful for dyeing heavily milled or felted fabrics, such as hat bodies for instance, as then the dye possesses greater penetrative properties and pa.s.ses more into the substance of the fabric, which is, therefore, better dyed through. Also they are suitable for dyeing half-wool fabrics as will be seen on referring to the chapter dealing with the dyeing of union or cotton-wool fabrics.
It is quite possible to dye a black on wool by using a combination of acid and azo dye-stuffs, and below is given a recipe ill.u.s.trating this method; it is one, however, rarely adopted.
_Blue-Black on Wool_.--Prepare the dye-bath with 10 lb. Glauber"s salt, 2 lb. Patent Blue, 6 oz. Brilliant Orange, 4 oz. Amaranth, 4 oz.
Acid Violet N, 4 lb. sulphuric acid. Enter the goods at about 150 F., raise to the boil and work to shade; lift, wash and dry. It may be of interest to note that by using a mixture of Azo Rubine and Acid green good blacks can be got.
There is a range of Acid and Azo dyes which are capable of dyeing from the usual acid baths on to wool, and yet can be developed and fixed on the fibre to good, full blacks. Types of such dyes are Anthracene Chrome Black F F, Diamond Black F, Chrome Patent Black D G and D G G, Fast Chrome Black, etc. Generally the blacks dyed on wool with these dyes are very fine, have a full, bloomy appearance, and are very fast.
They are much used in dyeing hat bodies and fine cloths which have to be very fast to the weather.