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 A
mordant
is required if the colour from natural
dyes is to remain washfast. Materials can be pre-soaked
in a mordant and left damp prior to dyeing or the mordant
can be added to the dyebath while the dye is being simmered.
Mordanting materials before and after dyeing with natural
dyes will add extra fastness.
The quantities of mordant used in preparing fibre for dyeing
have been the subject of much disagreement over recent years.
Historically the craft dyer used 'enough' to make sure the
job was done well. This gave rise in recent years to a strong
reaction for ecologically sound mordanting where the levels
of mordant were reduced considerably, alternative mordants
were sought out, and additives used to increase the effectiveness
of mordants. The most extreme version was the concept of 'dyeing
without chemicals'. The belief that oxalic acid used as a
mordant and derived directly from rhubarb leaves and roots
is 'good' and the same substance from a factory is 'bad',
is prejudiced. Oxalic Acid is a listed poison!
The common mordants are Alum
(Potassium Aluminium Sulphate), Copper
(Copper Sulphate), Chrome
(Potassium Dichromate), Tin
(Stannous Chloride), Iron
(Ferrous Sulphate) and Tannic
Acid. These are used in various combinations with
assistants for mordanting wool, cotton, linen and silk.
Before dyeing, it is important to check whether the
item is 'Prepared for Dyeing' (PFD) or requires scouring to
remove any grease, oil or starch. Run a few droplets of cold
water onto the fabric. If they soak in quickly, no scour is
necessary. To remove starches, size and oils, add 5mls of
Synthrapol
(a non-ionic detergent) along with 2-3 litres of water for
each 100gms of material. Stir gently over a 15 min period,
and then rinse thoroughly in warm water. It is possible to
use household detergent, but the alkaline residue may affect
the final colour or wash fastness.
Wool and Silk (Protein) Fibres
The quantities of mordants shown are for 500gm of dry weight
of woollen fibres with five litres of water. Bring the mixture
to boiling temperature and hold there for one hour, do not
agitate as this will felt the fibres. Allow to cool, rinse
and dry.
- Alum Mordant: 100gm, it helps to add
35gm of Cream
of Tartar (Potassium Hydrogen Tartrate - not
the substitute now sold for catering under the same common
name). Use of more than 150gm of Alum will tend to make
the fibre feel sticky.
- Copper Mordant: 100gm,
add 20gm of Cream of Tartar to improve colour and light
fastness.
- Chrome Mordant: 20gm,
there is no benefit from adding Cream of Tartar.
- Tin Mordant: 10gm, add
50gm of Cream of Tartar; excess tin will make woollen fibres
brittle.
- Iron Mordant: 20gm in
solution is added to the dye bath after dyeing to darken
the dye colour
Cotton and Linen (Cellulose) Fibres
 Cotton
and Linen dyeing requires a different approach. The metallic
part of the mordant does not attach readily to cellulose until
it has reacted with Tannic
Acid (tannin). First dissolve 40gm of Tannic Acid
in 5 litres of hot water and steep the fibres in the bath
for up to 24 hours.
To mordant the prepared fibres mix 250gm of Alum and 25gm
of soda
ash (anhydrous sodium carbonate) in 5 litres of
hot water and allow to soak for up to 24 hours, rinse in warm
water and dry and then repeat the mordanting. Copper, Chrome
and Tin mordants can be used in similar proportions as for
wool to assist with blues, blacks and reds.
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