Experimental Dyeing And Comparative Dye Testing





Every dyer ought to be able to make experiments in the mordanting and

dyeing of textile fibres for the purpose of ascertaining the best

methods of applying mordants or dye-stuffs, the best methods of

obtaining any desired shade, and for the purpose of making comparative

tests of dyes or mordanting materials with the object of determining

their strength and value. This is not by any means difficult, nor does

it involve the use of any expensive apparatus, so that a dyer need not

hesitate to set up a small dyeing laboratory for fear of the expense

which it might entail.



In order to carry out the work indicated above there will be required

several pieces of apparatus. First a small chemical balance; one that

will carry 50 grammes in each pan is quite large enough, and such a

one, quite accurate enough for this work, can be bought for 25s. to

30s., while if the dyer be too poor even for this a cheap pair of

apothecaries' scales might be used. It is advisable to procure a set

of gramme weights and to get accustomed to them, which is not by any

means difficult.



In using the balance always put the substance to be weighed on the

left-hand pan and the weights on the right-hand pan. Never put

chemicals of any kind direct on the pan, but weigh them in a

watch-glass, small porcelain basin, or glass beaker (which has first

been weighed), according to the nature of the material which is being

weighed. The sets of weights are always fitted into a block or (p. 212)

box, and every time they are used they should be put back into their

proper place.



The experimenter will find it convenient to provide himself with a few

small porcelain basins, glass beakers, cubic centimetre measures, two

or three 200 c.c. flasks with a mark on the neck, a few pipettes of

various sizes, 10 c.c., 20 c.c., 25 c.c.



The most important feature is the dyeing apparatus. Where only a

single dye test is to be made a small copper or enamelled iron

saucepan, such as can be bought at any ironmongers may be used; this

may conveniently be heated by a gas-boiling burner, such as can also

be bought at an ironmongers or plumbers for 2s.



It is, however, advisable to have means whereby several dyeing

experiments can be made at one time and under precisely the same

conditions, and this cannot be done by using the simple means noted

above.



To be able to make perfectly comparative dyeing experiments it is best

to use porcelain dye-pots (these may be bought from most dealers in

chemical apparatus), and to heat these in a water-bath arrangement.



The simplest arrangement is sketched in figure 33; it consists of a

copper bath measuring 15 inches long by 10-1/2 inches broad and (p. 213)

6-1/2 inches deep; this is covered by a lid on which are six apertures

to take the porcelain dye-baths. The bath is heated by two round

gas-boiling burners of the type already referred to.



The copper bath is filled with water which, on being heated to the

boil by the gas burners, heat up the dye-liquors in the dye-pots. The

temperature in the dye-pots under such conditions can never reach the

boiling point; where it is desirable, as in some cases of wool

mordanting and dyeing that it should be so high, then there should be

added to the water in the copper bath a quantity of calcium chloride,

which forms a solution that has a much higher boiling point than that

of water, and so the dye-liquors in the dye-pots may be heated up to

the boil.



An objection might be raised that with such an apparatus the

temperature in every part of the bath may not be uniform, and so the

temperature of the dye-liquors in the pots might vary also, and

differences of temperature often have a considerable influence on the

shade of the colour which is being dyed. This is a minor objection,

which is more academic in its origin than of practical importance. To

obviate it Mr. William Marshall, of the Rochdale Technical School, has

devised a circular form of dye-bath, in which the temperature in every

part can be kept quite uniform.



The dyeing laboratories of Technical Schools and Colleges are

generally provided with a more elaborate set of dyeing appliances.

These in the latest constructed consist of a copper bath supported on

a hollow pair of trunnions, so that it can be turned over if needed.

Into the bath are firmly fixed three earthenware or porcelain

dye-pots; steam for heating can be sent through the trunnions. After

the dyeing tests have been made the apparatus can be turned over and

the contents of the dye-pots emptied into a sink which is provided for

the purpose.



Many other pieces of apparatus have been devised and made for the (p. 214)

purpose of carrying on dyeing experiments on the small scale, but it

will not be needful to describe these in detail. After all no more

efficient apparatus can be desired than that described above.



Dyeing experiments can be made with either yarns or pieces of cloth,

swatches as they are commonly called; a very convenient size is a

small skein of yarn or a piece of cloth weighing 5 grammes. These test

skeins or pieces ought to be well washed in hot water before use, so

that they are clean and free from any size or grease. A little soda or

soap will facilitate the cleansing process.



In carrying out a dyeing test the dye-pot should be filled with the

water required, using as little as is consistent with the dye-swatch

being handled comfortably therein, then there is added the required

mordants, chemicals, dyes, etc., according to the character of the

work which is being done.



Of such chemicals as soda, caustic soda, sodium sulphate (Glauber's

salt), tartar, bichromate of potash, it will be found convenient to

prepare stock solutions of known strength, say 50 grammes per litre,

and then by means of a pipette any required quantity can be

conveniently added. The same might be followed in the case of dyes

which are constantly in use, in this case 5 grammes per litre will be

found strong enough.



Supposing it is desired to make a test of a sample of Acid Red, using

the following proportions, 2 per cent. dye-stuff, 3 per cent.

sulphuric acid and 15 per cent. Glauber's salt, and the weight of the

swatch which is being used is 5 grammes, the following calculations

are to be made to give the quantities of the ingredients required:--



For the dye-stuff, 5 (weight of swatch) multiplied by 2 (per cent. of

dye) and divided by 100 equals (5 x 2) / 100 = 0.1 gramme of dye.



For the acid we have similarly (5 x 3) / 100 = 0.15 gramme of (p. 215)

acid.



For the Glauber's salt (5 x 15) / 100 = 0.75 gramme of Glauber's salt.



These quantities may be weighed out and added to the dye-bath, or if

solutions are kept a calculation can be made as to the number of cubic

centimetres which contain the above quantities, and these measured out

and added to the dye-bath.



When all is ready the bath is heated up, the swatch put in and the

work of the test entered upon.



Students are recommended to make experiments on such points as:--



The shades obtained by using various proportions of dye-stuffs.



The influence of various assistants: common salt, soda, Glauber's

salt, borax, phosphate of soda in the bath.



The influence of varying proportions of mordants on the shade of

dyeing.



The value of various assistants, tartar, oxalic acid, lactic acid,

sulphuric acid, on the fixation of mordants.



The relative value of tannin matters, etc.



Each dyer should make himself a pattern book into which he should

enter his tests, with full particulars as to how they have been

produced at the side.



It is important that a dyer should be able to make comparative

dye-tests to ascertain the relative strength of any two or more

samples of dyes which may be sent to him.



This is not difficult but requires considerable care in carrying out

the various operations involved.



0.5 gramme of each of the samples of dyes should be weighed out and

dissolved in 100 c.c. of water, care being taken that every (p. 216)

portion of the dye is dissolved before any of the solution is used in

making up the dye-vats. Care should be taken that the skeins of yarn

or swatches of cloth are exactly equal in weight, that the same volume

of water is placed in each of the dye-pots, that the same amounts of

sulphate of soda or other dye assistants are added, that the

quantities of dye-stuffs and solutions used are equal, in fact that in

all respects the conditions of dyeing are exactly the same, such in

fact being the vital conditions in making comparative dye-tests of the

actual dyeing strength of several samples of dyes.



After the swatches have been dyed they are rinsed and then dried, when

the depths of shade dyed on them may be compared one with another. To

prevent any mistakes it is well to mark the swatches with one, two,

three or more cuts as may be required.



It is easier to ascertain if two dyes are different in strength of

colour than to ascertain the relative difference between them. There

are two plans available for this purpose; one is a dyeing test, the

other is a colorimetric test made with the solutions of the dyes.



#Dyeing Test.#--This method of ascertaining the relative value of two

dyes as regards strength of colour is carried out as follows. A

preliminary test will show which sample is stronger than the other;

then there is prepared a series of dye-vats, one contains a swatch

with the deepest of the two dyes, which is taken as the standard, the

others with the other dye but containing 2, 5 and 10 per cent. more

dye-stuff, and all these are dyed together, and after drying a

comparison can be made between these and the standard swatch, and a

judgment formed as to the relative strength of the two dyes; a little

experience will soon enable the dyer to form a correct judgment of the

difference in strength between two samples of dye-stuff.



The colorimetric test is based on the principle that the colour (p. 217)

of a solution of dye-stuff is proportionate to its strength. Two white

glass tubes, equal in diameter, are taken; solutions of the

dye-stuffs, 0.5 gramme in 100 c.c. of water, are prepared, care being

taken that the solution is complete. 5 c.c. of one of these solutions

is taken and placed in one of the glass tubes, and 5 c.c. of the other

solution is placed in the other glass tube, 25 c.c. of water is now

added to each tube and then the colour of the diluted liquids is

compared by looking through in a good light. That sample which gives

the deepest solution is the strongest in colouring power. By diluting

the strongest solution with water until it is of the same depth of

colour as the weakest, it may be assumed that the length of the

columns of liquid in the two tubes is in proportion to the relative

strength of the two samples. Thus if in one tube there are 30

centimetres of liquid and in the other 25 centimetres, then the

relative strength is as 30 to 25, and if the first is taken as the

standard at 100 a proportion sum may be worked out as follows:--



30: 25 :: 100 : 83.3;



that is, the weakest sample has only 83.3 per cent. of the strength of

the strongest sample.





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