SCIENCE / DESIGN
& TECHNOLOGY
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SCIENCE / DESIGN
& TECHNOLOGY |
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COMPARING NATURAL AND SYNTHETIC DYES
Curriculum links English National Curriculum:
Approximate time required: 2 hours Resources needed Per class of 30 children: Dyeing
naturally sheet Note: Turmeric produces a vibrant shade of yellow but requires about 30 minutes settling time after boiling in the dyebath. Chamomile (available as tea bags from health food shops) also produces a yellow dye and can be strained in seconds.
Organisation Initial class discussion followed by group work. Advance preparation The strip of multi-fibre should be cut into 10 x 10 cm squares. The 'acetate' end of each square should be marked in some way, e.g. indelible ink. Otherwise, it is hard to identify the fibre once the identification label has been removed. If a lack of time, supervision or equipment does not permit the children to extract dyes, these can be prepared before the lesson and displayed in transparent, sealed containers alongside their sources. Carrying out the activity A display of plants, vegetables and flowers, whose
colours are used in dyes, makes an attractive starting point for this
activity and provides a useful focus for discussion of natural dyes. For
ideas on which plants to include, go to the Background Information below
and Sources for Natural Dyestuffs. Recipe for a natural dye The leaves/flowers, etc. used to obtain the colour are referred to as the dyestuff.
1. Pour the water in an old pan and add the
dyestuff. Dyeing the fabric with a natural dye
Dyeing the fabric with a synthetic dye Instructions for use are given in the packet. A packet of fixative and kitchen salt (4 tablespoons per packet) are required when using cold water dyes. The fabric is steeped in the dyebath for an hour, stirring for the first 10 minutes. The fabric is rinsed in cold water (as for the natural dyes), rather than washed in soapy water. Comparing the dyes Once the fabric is dyed and dried, the groups cut and attach strips of the fabric to their Dyeing naturally record sheet, to make a visual comparison. Children also use the sheet to record their observations about the colours produced by the two dyes on the different fabric types. A colourful collective display can be made of the results of the investigations, showing the colours and how they were obtained. Background information Plants or flowers giving a colour-fast dye are called substantive and those needing a fixative are called fugitive. A classroom display of dyestuffs could be divided into these two categories. Substantive dyes
Fugitive dyes
There are many other plants, barks and flowers that can be used. Flowers offer interesting dyestuffs, as the majority give shades of yellow or green; even though the flowers themselves may naturally be bright and vivid! Natural dyes have been used for thousands of years. The first commercial synthetic dye was discovered in 1856 in the UK by William Henry Perkin. It was a purple dye, often referred to as Perkin's Purple. Until this dye was discovered, a dress dyed purple could start fading in a few hours! The book 'Mauve' by Simon Garfield tells the story (pub. Faber) ISBN 0-571-20197-0. Synthetic dyes give bright and vivid colours, many natural dyes do not. A greater range of colours and shades is available from synthetic rather than natural dyes. Comparing the colours produced with a commercial colour chart emphasizes this point. The same dye has quite different effects on different fabrics. For example, some synthetic dyes are made specifically to dye cotton or others to dye acrylic, and will not colour other fabrics or will not produce the desired colour on other fabrics. The multi-fibre fabric used in this activity is produced for the colour industry for testing dyes.
It has a very high specification for each fabric and industry uses it to test the quality and effectiveness of dyes. In this way, they can ensure that the high standards required of their dyes are met. Extensions / links Science |
