Dyeing of textiles
Practical Action
Protective equipment. Gloves for holding hot pans will prevent burns. An apron will
protect your clothing. Rubber gloves will prevent skin irritation caused by mordants, and
will also prevent you from dyeing your hands. A face mask can cut down the amount of
fumes or powder inhaled during the dyeing process.
Mordants
Few natural dyes are colour-fast with fibres. Mordants are substances which are used to fix
a dye to the fibres. They also improve the take-up quality of the fabric and help improve
colour and light-fastness. The term is derived from the Latin mordere, to bite. Some natural
dyes, indigo for example, will fix without the aid of a mordant; these dyes are known as
‘substantive dyes’. Others dyes, such as madder and weld, have a limited fastness and the
colour will fade with washing and exposure to light.
Traditionally, mordants were found in nature. Wood ash or stale urine may have been used
as an alkali mordant, and acids could be found in acidic fruits or rhubarb leaves (which
contain oxalic acid), for example. Nowadays most natural dyers use chemical mordants
such as alum, copper sulphate, iron or chrome (there are concerns, however about the toxic
nature of chrome and some practitioners recommend that it is not used).
Mordants are prepared in solution, often with the addition of an ‘assistant’ which improves
the fixing of the mordant to the yarn or fibre. The most commonly used mordant is alum,
which is usually used with cream of tartar as an additive or assistant. Other mordants are:
Iron (ferrous sulphate)
Tin (stannous chloride)
Chrome (bichromate of potash)
Copper sulphate
Tannic acid
Oxalic acid
Using a different mordant with the same dyestuff can produce different shades, for
example;
Iron is used as a ‘saddener’ and is used to darken colours.
Copper sulphate also darkens but can give shades which are otherwise very difficult to
obtain.
Tin brightens colours.
Tannic acid, used traditionally with other mordants, will add brilliancy.
Chrome is good for obtaining yellows.
Oxalic acid is good for extracting blues from berries.
Cream of Tartar is not really a mordant but is used to give a lustre to wool.
Mordants are often poisonous, and in the dye-house they should be kept on a high shelf out
of the reach of children. Always use protective clothing when working with mordants and
avoid breathing the fumes.
The mordant can be added before, during or after the dyeing stage, although most recipes
call for mordanting to take place prior to dyeing. It is best to follow the instructions given in
the recipe being used or experiment on a sample before carrying out the final dyeing. Later
in this brief we will explain how the mordant is mixed and used as part of the dyeing
process.
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