copperas and 20 per cent. of cream of tartar is a mordant used for some colours.

4 per cent. copperas, 10 per cent. cream of tartar gives good olive colours with weld.

8 per cent. copperas without tartar with single bath method, for dark olive brown with old fustic.

2 oz. copperas and 2 oz. cream of tartar to 2½ lbs. wool.

2 oz. copperas, 1½ oz. oxalic acid to 2½ lbs. wool.

TIN.—(Stannous chloride, tin crystals, tin salts, muriate of tin.)

Tin is not so useful as a mordant in itself, but as a modifying agent with other mordants. It must be always used with great care, as it tends to harden the wool, making it harsh and brittle. Its general effect is to give brighter, clearer and faster colours than the other mordants. When used as a mordant before dyeing, the wool is entered into the cold mordanting bath, containing 4 per cent. of stannous chloride and 2 per cent. oxalic acid: the temperature is gradually raised to boiling, and kept at this temperature for 1 hour. It is sometimes added to the dye bath towards the end of dyeing, to intensify and brighten the colour. It is also used with cochineal for scarlet on wool, in the proportion of 6 per cent. of stannous chloride and 4 per cent. of cream of tartar. Boil for 1 to 1½ hours. Then wash well. The washing after mordanting is not always essential. Also 6 to 8 per cent. of oxalic acid and 6 per cent. of stannous chloride, for cochineal on wool. This mordant produces bright fast yellows from old fustic, by boiling the wool from 1 to 1¼ hours, with 8 per cent. of stannous chloride and 8 per cent. of cream of tartar. One recipe gives 2 oz. tin and 4¼ oz. cream of tartar to 2½ lbs. wool in 10 gallons of water. It is not a suitable mordant alone for cotton, but can be used to brighten the colour in combination with other mordants. "The nitro-muriate of tin (dyer's spirit) although it produces good yellows with quercitron bark, produces them in a much weaker degree than the murio-sulphate of that metal, which is really the cheapest and most efficacious of all the solutions or preparations of tin for dyeing quercitron as well as the cochineal colours." —Bancroft.

CHROME. (Potassium dichromate, Bichromate of Potash.)

Chrome is a modern mordant, unknown to the dyer of 50 years ago. It is excellent for wool and is easy to use and very effective in its action. Its great advantage is that it leaves the wool soft to the touch, whereas the other mordants are apt to harden the wool. In commercial dyeing it is now almost exclusively used, as it has proved itself the most generally convenient. By some it is said not to be so fast to light as the other mordants, but it produces brighter colours. The wool should be boiled for one to one & a half hours with bichromate of potash in the proportion of 2 to 4 per cent. of the wool. It is then washed well and immediately dyed. Wool mordanted with chrome should not be exposed to light, but should be kept well covered with the liquid while being mordanted, else it is liable to dye unevenly. An excess of chrome impairs the colour. 3 per cent. of chrome is a safe quantity to use for ordinary dyeing. One recipe gives 1½ oz. of chrome to 2½ lbs. of wool. It should be dissolved in the bath while the water is heating. The wool is entered and the bath gradually raised to the boiling point, and boiled for three quarters of an hour.

In the dyeing of cotton, it is used for catechu browns and other colours. The cotton is soaked in a decoction of catechu, and afterwards passed through a boiling solution of chrome, or it is worked for half an hour in a bath of chrome at 60°C., and then washed. It is usual to wash wool or cotton after mordanting with chrome, but some dyers do not think it necessary.

COPPER. (Copper Sulphate, Verdigris, blue vitriol, blue-stone.)

Copper is rarely used as a mordant. It is usually applied as a saddening agent, that is, the wool is dyed first, and the mordant applied afterwards to fix the colour. With cream of tartar it is used sometimes as an ordinary mordant before dyeing, but the colours so produced have no advantage over colours mordanted by easier methods.

Examples.—6 per cent. of copper is used as a mordant for weld to produce an olive yellow. 4 to 5 per cent. is used with old fustic for yellow. 10 per cent. of copper gives to wool a reddish purple with cochineal.

Mordants should not affect the physical characteristics of the fibres. Sufficient time must be allowed for the mordant to penetrate the fibre thoroughly. If the mordant is only superficial, the dye will be uneven: it will fade and will not be as brilliant as it should be. The brilliancy and fastness of Eastern dyes are probably due to a great extent to the length of time taken over the various processes of dyeing. The longer time that can be given to each process, the more satisfactory will be the result.

Different mordants give different colours with the same dye stuff. For example:—Cochineal, if mordanted with alum, will give a crimson colour; with iron, purple; with tin, scarlet; and with chrome or copper, purple. Logwood, also, if mordanted with alum, gives a mauve colour; if mordanted with chrome, it gives a blue. Fustic, weld, and most of the yellow dyes, give a greeny yellow with alum, but an old gold colour with chrome; and fawns of various shades with other mordants.

TANNIN.—(Tannic Acid.)—Tannins are used in the dyeing of cotton and linen. Cotton and linen possess the remarkable power of attracting tannins from their aqueous solution, and when these substances are prepared with tannins, they are able to retain dyes permanently. Cotton saturated with tannin, attracts the dye stuff more rapidly, and holds it. Tannic acid is the best tannin for mordanting cotton and linen, as it is the purest and is free from any other colouring matter. It is, therefore, used for pale and bright shades. But for dark shades, substances containing tannic acid are used, such as sumach, myrobalans, valonia, divi-divi, oak galls, chestnut (8 to 10 per cent. of tannin), catechu.

Cotton and linen are prepared with tannin after they have been through the required cleansing, and if necessary, bleaching operations. A bath is prepared with 2 to 5 per cent. of tannic acid of the weight of the cotton, and a sufficient quantity of water. For dark shades, 5 to 10 per cent. should be used. The bath is used either hot or cold. It should not be above 60°C. The cotton is worked in this for some time, and then left to soak for 3 to 12 hours, while the bath cools. It is then wrung out and slightly washed.

The following gives the relative proportions of the various substances containing tannin:—1 lb. tannin equals 4 lbs. sumach, 18 lbs. myrobalans, 14 lbs. divi-divi, 11 lbs. oak galls.

A few examples taken from various recipes of cotton dyeing:—

For 10 lbs. cotton use 12 oz. tannin.
For 50 lbs. cotton use 10 lbs. sumach.
For 40 lbs. cotton use 10 lbs. sumach.
For 20 lbs. cotton use 2 lbs. yellow catechu or black catechu.
For 20 lbs. cotton spend 3 lbs. of catechu with 3 oz. of blue vitriol.

Some recipes soak the cotton for 24 hours, others for 48 hours.

CHAPTER IV.


BRITISH DYE PLANTS

The introduction of foreign dye woods and other dyes during the 17th and 18th centuries rapidly displaced the native dye plants, except in certain out of the way places such as the Highlands and parts of Ireland. Some of these British dye