Mordants used with Natural Dyes
Below is a list of mineral mordants commonly used today with natural dyes. The term 'mordant' derives from a french word meaning 'to bite' the fiber - describing how mordants were thought to work. In reality, it is still not really understood how a mordant helps dye adhere better to fiber.
In early days the leaves and roots of certain plants were used. This is the case even now in India and other places where traditional dyeing methods are still carried on. An example of this is the eco-friendly
Blue Castle Fiber Arts.
Alum has been known for centuries in Europe. Alum and iron are the most environmentally friendly of the mineral mordants while chrome, tin and copper are considered more toxic. Some additional chemicals used with natural dyes, like cream of tartar, acetic acid and vinegar as well as the plant based mordants and tannic acid are also safe to use.
There are two processes concerned with the dyeing of most colours; the first is mordanting and the second is the colouring or actual dyeing. The mordanting prepares the stuff to receive the dye (mordere, to bite).
Any natural dye belongs to one of two classes. Substantive, giving colour directly to the material: and adjective, which includes the greater number of dyes and requires the use of a mordant to bring out the colour. All adjective dyes need this preparation of the fibre before they will fix themselves on it. The use of a mordant, though not a necessity, is sometimes an advantage when using substantive dyes.
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 natural 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 natural 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.
Silk and wool require very much the same preparation except that in the case of silk, high temperatures should be avoided. Wool is generally boiled in a weak solution of whatever mordant is used. With silk, as a rule, it is better to use a cold solution, or a solution at a temperature below boiling point. Cotton and linen are more difficult to dye than wool or silk. Their fibre is not so porous and will not hold the natural dye stuff without a more complicated preparation. The usual method of preparing linen or cotton is to boil it first with some astringent. The use of astringents in dyeing depends upon the tannic acid they contain. In combination with ordinary mordants, tannic acid aids the attraction of the colouring matter to the fibre and adds brilliancy to the colours. The astringents mostly used are tannic acid, gall nuts, sumach and myrobalams. Cotton has a natural attraction for tannic acid, so that when once steeped in its solution it is not easily removed by washing.
(aluminum potassium sulfate)
This is the most generally used of all the mordants, and has been known as such from early times in many parts of the world. For most colours a certain proportion of cream of tartar should be added to the alum bath as it helps to brighten the ultimate colour. The usual amount of alum is a quarter of a pound to a pound of wool (25% of the weight of wool). As a rule, less mordant, (as little as 10% of the weight of wool) is needed for light colours than for dark. Excess of alum is apt to make the wool sticky. The usual length of time for boiling is about an hour. Some dyers give as much as 2-1/2 hours. There is also a cold method whereby the wool is added to a cold alum bath and left for one to two weeks.
Example of mordanting with alum—1/4 lb. of Alum and 1 oz. cream of tartar for every pound of wool (metric: 125 gms alum and 30 gms cream of tartar for every 500 gms of wool). This is dissolved and when the water is warm the wool is entered. Raise to boiling point and boil for one hour. The bath is then taken off the fire and allowed to cool over night. The wool is then wrung out (not washed) and put away in a linen bag in a cool place for 4 or 5 days, when it is ready for dyeing, after being thoroughly washed.
(Ferrous Sulphate, copperas, green vitriol)
Iron is one of the oldest mordants known and is largely used in wool and cotton dyeing. It is almost as important as alum. The temperature of the mordanting bath must be raised very gradually to boiling point or the wool will dye unevenly. A general method of dealing with copperas is to boil the wool first in a decoction of the colouring matter and then add the mordant to the same bath in a proportion of 5 to 8 per cent of the weight of the wool, and continue boiling for half an hour or so longer. With some dyes a separate bath is needed, such as with Camwood or Catechu. Great care is needed in the using of copperas, as, unless it is thoroughly dissolved and mixed with the water before the wool is entered, it is apt to stain the wool. It also hardens wool if used in excess or if boiled too long. A separate bath should always be kept for natural dyes or mordants containing iron. The least trace of it will dull colours and it will spoil the brilliancy of reds, yellows and oranges.
Copperas is mostly used for the fixing of wool colours (Fustic, etc.) to produce brown shades; the wool being boiled first in a decoction of the natural dye for about 1 hour, and then for 1/2 an hour with the addition of 5 to 8 per cent of copperas. If used for darkening colours, copperas is added to the bath after the dyeing, and the boiling continued for 15 to 20 mins.
(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 always be 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 mordant 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 natural 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 one bath method.
(Potassium dichromate. Bichromate of Potash.)
Chrome is a modern mordant. 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. The disadvantage is that chrome is considered an environmentally toxic mordant and must be disposed of properly. For this reason, many natural dyers choose not to use chrome.
The wool should be boiled for 1 to 1-1/2 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 recommended quantity to use for ordinary dyeing. 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 3/4 of an hour.
(Copper Sulphate, Verdigris, Blue Vitriol, Blue Copperas, Bluestone)
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.
Adapted from: VEGETABLE DYES: Being a Book of Recipes and Other Information Useful to the Dyer by ETHEL M. MAIRET
*If you are considering using chrome or potassium dichromate (bichromate of potash), tin (stannous chloride) or copper (copper sulphate) with your natural dyes, read this article first -
WHY WE DON'T USE CHROME ANYMORE!
by Darvin DeShazer, USA(The International Mushroom Dye Institute)
See Blue Castle Natural Dye Catalogue
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