Natural dyeing

This experiment should take around 60 minutes to dye the cloth after planning. This experiment is best carried out during autumn. 

Equipment

• Eye protection
• Clothing protection/lab coats
• Beakers (all sizes)
• Pestles and mortars
• Glass stirring rods
• Tongs
• String
• Buckets for rinsing cloth
• Bunsen burners
• Tripods
• Gauzes
• Heatproof mats
• Clamp stands
• Undyed woollen cloth (appeal for a very old blanket). Alternatively, cotton may be used.
• A selection of plant material, eg onion skins, red cabbage, beetroot, rhododendron leaves, acorns, used coffee grounds, pine cones, blackberries, redcurrants.
• Mordanting salts: eg potassium aluminium sulphate(alum), iron(ll) sulphate, copper(ll)sulphate, tin(ll)chloride. 

Health, safety and technical notes

• Read our standard health and safety guidance here.
• Wear eye and clothing protection.
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• Warn students about danger from boiling liquids and steam.
• Care should be taken if pupils go to collect their own plant samples, to ensure they don’t pick dangerous plants such as hogweed or deadly nightshade.
• Potassium aluminium sulphate(alum), AlK(SO₄)₂.12H₂O is of low hazard. See CLEAPSS Hazcard HC002b.
• Iron(II) sulphate FeSO₄.7H₂O is harmful if swallowed and a skin/eye irritant. See CLEAPSS Hazcard HC055b.
• Copper(II) sulphate, CuSO₄ is causes eye damage, is harmful if swallowed and is HAZARDOUS to the aquatic environment. See CLEAPSS Hazcard HC027c.
• Tin(ll) chloride, SnCl₂ is CORROSIVE to skin and eyes, harmful if swallowed and hazardous to the aquatic environment. See CLEAPSS Hazcard HC102a.
• It is probable that the dyeing solution will be of low hazard unless some of the mordanting salts are used at very high concentration. 

Possible approaches

Dyeing can be used to supplement a unit on plants or one on colour & light, or it could be part of a cross-curricular unit on ancient civilisations.

The dye is extracted by simmering a large quantity of the plant (flowers, berries, leaves or bark) in water. To create a stronger bond between the dye and the material, dyers often use mordants (ie fixing agents).

As well as helping the dyes stick to the fibre, mordants also increase the colour range of the dye (many dyes give different colours with different mordants).

Copper or iron pots may also act as mordants and affect the colour of the dye. You could add cream of tartar (acid potassium tartrate) to your materials list - it is used as an additive to brighten the colours. 

Possible extension

It is fun to dye other fabrics apart from wool, eg silk, cotton etc.

Staple pieces of the various cloths together and immerse in the dye-bath. Natural dyes work best with natural fibres.

Find out about synthetic dyes (1850s onwards). Students use dyed silk in various art projects: eg make a colourful scarf or tie using the knowledge they have gained. A T-shirt promoting chemistry could be produced.

Colour-fastness: Investigation of whether coloured cloth affected by light, heat, chlorine (important for swimwear) or perspiration? 

Notes

If copper or tin salts are used as mordants (or chromium) then solutions should be kept for disposal rather than washed down the sink. (It may be easier to precipitate as the carbonate, filter and store the solid). 

There is a large quantity of stained glassware to wash up, and some dyes are very difficult to remove.