Mordants for natural dyes are often required to help fix the dye to the fiber. 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.
Natural dyes belong to one of two classes. Substantive, which do not require a mordant, and adjective, which includes the greater
number of dyes and requires the use of a mordant to bring out and fix the
color. All adjective dyes need this preparation of the fiber before
they will fix themselves on it. For substantive dyes, the use of a mordant, though not a
necessity, is still sometimes an advantage, particularly to obtain a variety of shades.
Mordants come from primarily two groups - plant based, especially plants high in tannins and mineral based such as alum, iron, tin and chrome.
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.
Mordants should not affect the physical characteristics of the fibres.
Sufficient time should be allowed for the mordant to thoroughly penetrate the fiber. 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 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 - above 80C (176F) - 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 fiber is not as porous and will not hold the natural dye without a more complicated preparation - that is when using the most commonly known mordants. The usual method of preparing linen or cotton is to boil it first with an astringent such as tannic acid or a mordant high in tannins such as myrobalan, sumach or gall nuts and then following with a mineral mordant. Cotton has a natural attraction for tannic acid, so once steeped in its solution it is not easily removed by washing. Tannic acid aids the attraction of the coloring matter to the fiber and adds brilliancy to the colors.
There are two mordants for cotton type fibers that can simplify the process to just one step. One is myrobalan extract, available from Blue Castle Fiber Arts as "Natural Mordant" and the other is Aluminum acetate in place of the more common Alum sulphate. They are slightly more expensive but the results are worthwhile.
Some substantive dyes:
Navy Blue and Forest Green from Blue Castle Fiber Arts
Indigo is substantive but requires the Indigo Vat Method
Although these dyes do not require a mordant, mordants can still be used to broaden the range of colors and increase colorfastness.
Blue Castle Fiber Arts is a small on-line fiber arts business and importer of natural dyes from India. We are located on the beautiful shores of Lake Ontario in Hamilton, Ontario, Canada.
This website focuses on our easy-to-use natural dyes and you will find plenty of information about them and how to use them. You can also visit our supplier's website here: Sam Vegetable Colours.