COSHH SHEET 47
DYES AND MORDANTS
Applicable to: natural dyes; reactive dyes; alum and ferrous sulfate etc.
Cold water dyes: Textiles may be prepared in one of several ways and then
left to soak in a room-temperature dye bath.
Hot water dyes: Quicker results can be achieved by using a hot dye bath.
Dyeing with mordants: Some fabrics must be pretreated with a mordant to
make the coloured dye stick to the fibres, e.g. alum, ferrous sulfate, tin (II)
chloride, potassium dichromate.
Some dyes, e.g. Disperse Yellow, have produced cancers, or are suspected
as cancer-causing agents. They are now labelled Toxic. Potassium
dichromate (VI) is carcinogenic by inhalation (of the dust) and toxic if
swallowed. If such dyes are used with the care normally taken when handling
chemicals, there should be no long term adverse health effects.
Some mordants, e.g. iron (II) (ferrous) sulfate and tin (II) (stannous) chloride
are harmful if swallowed. Iron (II) sulfate has an OES of 2 mg/m3; tin (II)
chloride OES is 4 mg/m3 (15 min ref period). When solutions are being used
as mordants, they are unlikely to give rise to spray at these concentrations
but there could be a problem when preparing solutions.
Some dyes and dye fixatives, e.g. containing sodium silicate and mordant
solutions containing more than 7% potassium dichromate (VI) are irritant to
Certain reactive dyes have been identified as giving rise to allergy and/or
sensitisation. Potassium dichromate (VI) solutions (of less than 0.5%) may
cause sensitisation. Procion yellow MX-8G is more likely than others to
trigger a response. The hazard is greatest when handling the solid dye;
solutions are much safer.
Some mordants such as alum (aluminium potassium sulfate) are not classified
Containers of toxic materials should be opened and the solid weighed out in a
laboratory fume cupboard; once covered with water the risk becomes minimal.
Gloves and eye protection should be worn.
When using dyes, fixers and mordants that are irritant, the eyes should be
protected with safety spectacles from the risk of splashes and dust. Procion
MX dyes should be avoided; Procion HE dyes are safer. In most cases,
gloves alone will provide sufficient protection from irritation.
When handling mordant solutions and reactive dyes in solid form, gloves will
usually provide sufficient protection from sensitisation. If Procion MX dyes are
used, they should be handled in a fume cupboard.
Pupils should handle dyes in solution rather than as solids. If powdered dyes
must be employed, they should not be used below Year 9 and then only with
close supervision below Year 12. Pupils should not be allowed to handle the
powder of very reactive dyes, such as Procion Yellow MX-8G.
All dyes, fixers and mordants should be kept away from food areas in a
secure place. It may be sensible to store mordant chemicals along with
similar substances in the science department. Potassium dichromate (VI) and
its solutions are oxidising agents which will assist fire; store them away from
flammable and other combustible materials.
Small quantities of unwanted dyes are best made into solutions and flushed
away. Large quantities should be disposed of by an authorised waste
Immediate Remedial Measures
If swallowed: Give plenty of water and seek medical attention. DO NOT
If dye or mordant is in the eyes: Obtain medical attention. Irrigate immediately
with water, holding eyelids apart and continue until the casualty reaches
If spilt on the skin or clothes: Remove contaminated clothing. Wash affected
area thoroughly with a large amount of water. If a large area of skin is
affected, seek medical attention. Soak contaminated clothing and rinse
Allergic reaction: If the casualty shows anxiety, red, blotchy skin, swelling of
the face and neck and puffiness around the eyes, they could be suffering from
a serious allergic reaction. Call an ambulance and prop the casualty in a
sitting position in case breathing problems develop.