BLACK BY SUBSEQUENT FIXING

This is generally carried out in a series of course tanks. The dry unbleached cloths go through a first tank containing a boiling solution of Logwood extract or a mixture of Logwood and a tanning extract, duly alkalized. After this, they are folded back on tip trucks where they rest during five or six hours at least.

Thus they go in a second tank containing a tepid solution (40 to 50°C) of iron salt, then, after a new rest of a few hours, in a third tank with two compartments. The first one is for liming and the second one is for the rinsing.
It is then enough to bring these parts in a hot alkalized solution of Logwood, either on jigger or in a fourth tank.

When the bottoming is carried out exclusively with Logwood, the first tank must be assembled in a bath containing 8 to 10 kilos of extract at 30° Baumé and 250 to 300 g of Solvay soda per hectolitre of water. The addition of a tanning extract is made in substitution of a part of the Logwood extract, and the proportion of each can reach 50/50.

The second tank, for fixing, is built with a solution of iron salt (pyrolignite, sulphate or nitrosulphate). At the beginning, the bath must indicate 3° Baumé. During the process, one nourishes it by addition of a strong solution, capable to maintain the initial iron content. One often uses a mixture of the above mentioned salts, especially the pyrolignite and the nitrosulphate.
For the liming, the first compartment of the third tank is filled with whitewash heated at approximately 80°C. One must maintain the bath milky enough to be assured that it constantly contains free lime, essential condition for the fixing of ferric oxide.

BLACK BY DYEING ON MORDANT FIXED BEFOREHAND

This method consists in mordanting directly the dry unbleached cloths by impregnating them with iron pyrolignite at 5° Baumé, heated at 50/55°C.

When the operation is done on pad, one should make at least three passages in order to ensure a good penetration of the mordant. If the process is carried out in a course tank, two passages are enough thanks to the intermediate rest. The fabrics thus mordanted are dried either by suspending them on slats in a drying room, or by passing them through a hotflue.
Once dry, the mordanted pieces, sewn end to end, are degummed, at the speed of 40 meters per minute, in a course tank containing a whitewash heated to a temperature close to boiling. Take care to nourish the bath during the process, by addition of more concentrated whitewash when each seam comes by.

Coming out of liming, the degummed fabrics are immediately a thorough washing while passing in ropeform. One separately folds back each piece for the dyeing which is also carried out in ropeform, in tanks known as "à garancer".

Each one of these tanks contains ten pieces tied without end, each one separately. They turn during nineteen minutes in a Logwood bath slightly alkalized with one liter of Logwood extract 30° Baumé for 10 kg of fabric.
Raise the temperature little to little, through a steam bubbler, so as to come to a boiling temperature after one hour. Then one continues the dyeing during half an hour, with a moderate bubble.
The bath is then emptied and the tank is filled with fresh water for the rinse and the cooling of the fabrics which one then racks with an untwister or a scutcher, in order to be able to dry them on rolls, before giving them the finish.

CONTINUOUS DYEING

This process is based on traditional method (b) of preliminary ferric oxide fixing on the fabric. It consists :

1 - to impregnate the fabric with iron pyrolignite
2- to dry it
3- to degumm it with lime water
4- to rinse it
5- to dye it with Logwood

the whole operation in only one passage

If one does not have the necessary installation, work can be stopped in some of its phases, without the process ceasing to be continuous.
The facilities which have drying yarns, can continue to dry the parts mordanted with pyrolignite and then to clean them and to dye them in the five compartment of the course tank which constitutes the principal advantage of the continuous process.

Mordanting :

The unbleached cloths, dry and roasted if necessary, are impregnated directly by a passage in a course tank containing iron pyrolignite 5° Baumé, heated at 45/50°C.

After two successive squeezings, the goods are folded back in tip trucks. Then, after a few hours rest, in order to finalize the fibre penetration, the fabric passes in a pad whose basin contains pyrolignite of same concentration, so as to equalizing the impregnation and to express it very strongly.
The mordant excess thus recovered is used to supply the impregnation tank. If drying is made through the hotflue, this exprimor pad must be in the front and uninterrupted with the drier. On the other hand, if one dries through drying room, the pad must roll up the mordanted fabrics into transportable rollers.

Drying of the mordanted pieces :

As already mentioned, the two most suitable drying methods for this are : the hotflue and the drying yard. The advantage of the first system is to allow a continuous process, without having to un-stitch the parts. As for the second, it is does not require heating but requires a surplus manpower compared to mechanical drying. Let us add that the colours obtained by mordant dyeing dried by contact always come out more or less two-sided, and that the iron oxide thus fixed, losing its affinity for the colouring matters, draws badly in dyeing and gives only a bronzed and very thin black.

Liming, rinsing and dyeing :

These three last phases of the continuous dyeing take place in a course tank with five compartments. This tank is made of coated with roll of brass turning ; it is surmounted by five couples of squeeze rolls whose inferiors are covered with brass shirts, and the superiors of half-hard rubber shirts. Streching screws, turning to wrong way of the walk of fabric, are to the entry of each of the five groups of squeezers infallibly opening all the folds of fabric and the rolled edges.

The first compartment (lime degumming) is heated by a bubbler. The two following compartments are used for washing; they are laid out in cascades. The water squirts to the entry of the squeezers, runs out in the opposite direction of the walk of the piece and is evacuated by overflow.

The last two compartments are used for dyeing ; they are at different levels so that the overflow of the fifth can run out in the fourth. In the bottom there's a copper steam coil, fit with a drain cock, which heats the two baths by contact, in order not to dilute them with condensed water of the steam.
Here is the process with the five compartment tank :

The fabrics, mordanted and dried, enter the boiling lime bath which purpose is to supplement the iron oxide fixing on the fabric, and to peroxidize it. Afterwards, the pieces go into the two washing compartments where they get rid of all the soluble salts. Finally, in the two dyeing compartments, they are impregnated with alkalized Logwood, in sufficient quantity to saturate the fixed mordant.

When coming out of the machine, the goods are folded back in tip trucks where they rest for the necessary time to get a perfect combination of hematein and ferric oxide. This combination, favoured by the heat of the passage in boiling bath, can be regarded as perfect after a two hours rest. One can then proceed to the final rinse which is given on a squeezer exprimor. Then the pieces are dried in drums.

With regard to liming, one cannot indicate exactly the proportions of lime to use. One starts by filling the tank to clean up almost entirely with boiling water. Then, add to it 20 to 25 liters of a whitewash, prepared by watering 25 kilos of quicklime in 500 liters of water. Then, during the operation, one nourishes the bath by addition of 4 to 5 liters of whitewash, each time that it does not contain enough free calcic hydrate to be able to easily neutralize the acids which the drying did not eliminate and which still exist in a sub-salt state in the fabric to clean up.
However, one easily witnesses the disappearance of the lime hydrate, first when the bath loses its milky aspect, and then when, by degumming, the greenish-gray colour of the mordanted fabric does not change as quickly any more into a dark rust shade, evidence of a good fixing of the ferric oxide. It is necessary, however, to avoid an excess of lime.

Regarding the dyeing, the preparation is made by mixing 22 kg of pure Logwood N.O. extract diluted in 50 liters of water with a solution of 1 kilo of soda salt, in a barrel containing enough boiling water to give a 200 liter preparation.

One prepares, once and for all, the two dyeing tank compartments by introducing a sufficient quantity of water to cover the inferior rolls. This is heated and in each compartment are added 25 liters of the above-mentioned preparation. Then, for each incoming piece, 5 liters of the same preparation are shared between the two compartments. Of course, the quantity of logwood necessary to nourish and maintain the concentration of the dyeing bath is correlated with the quality of the fabric. The proportions indicated above are for parts weighting 10 to 11 kilos for 100 meters. They will have to be increased according to the weight of the fabrics.
During the whole process, the Logwood bath must be maintained close to boiling temperature. One thus activates considerably the formation of black lacquer in the fiber and the excess dye which the fabric takes with it makes it possible to perfect the ferric oxide saturation during the rest.

Undoubtedly, the level of the dyeing baths is increased by the mixture of the preparation and the water taken by the pieces when coming out after the rinse. It must be stabilized by the overflows which pour from the fifth tank into the fourth and from this one into a barrel. This evacuated bath is used for new preparations.

There comes a time when the Logwood bath, having accumulated impurities of all kinds (layers of sediment, Logwood lacquer, etc) needs to be renewed. In this case, one empties of its content the compartment N°4 and, after having cleaned it well, one siphons the limpid part of the contents of N° 5, while avoiding touching the deposit which is then evacuated. After cleaning, one fills up this last compartment with a fresh bath.

Through this process, the consumption of products and work force is as reduced as possible, considering nothing is lost. One counts, for the dyeing of 10 kilos of cotton fabrics in intense and tight black, approximately :

- 3 L iron pyrolignite 16-17° Baumé
- 120 g of quicklime
- 475 g of pure Logwood N.O. extract
- 35 g of Solvay soda salt

The lining articles, dyed through the continuous process, offer a beautiful solid black, with no change of shade in the stores. Furthermore, the beauty and the resistance of this black are still increased when one slightly colours the finish of these articles by adding, for 500 liters : 1 liter of Logwood extract 30° Baumé, 75 g of sodium dichromate and 75 g of copper sulphate.

Stiffened articles and lawns for hat industry:

In the production of certain black articles very strongly finished, requiring consequently the application of a lot of very coloured finishes, the light fabrics are dyed only with a black of little intensity (ie to some extent a very dark gray).
In this case, the application of the first two operations of the process of dyeing in black by subsequent fixing, is quite indicated. It can be summarised as follows : impregnation of the fabric in alkalized Logwood, rest, fixing with iron pyrolignite, rest, final rinse. There is no need of other treatment.