ART / DESIGN & TECHNOLOGY
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ART / DESIGN & TECHNOLOGY
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Decolourising
Curriculum links English National Curriculum:
Approximate time required: 90 minutes Resources needed These depend on whether fabric is dyed in the classroom (see Dyeing Techniques), or a piece of non-fast coloured fabric is obtained for use in this activity: If dyeing own fabric: If obtaining non colour-fast fabric: 5ml waste water from dyeing process, 5ml blue
food colouring Common to both fabric types: 250ml Water Suggested organisation Two adult demonstrations followed by individual work. Carrying out the activity
Decolourising demonstration 1. Dilute 5ml of blue food colouring in 250ml of water in a clear container to simulate coloured waste water from a factory dyebath process (or 250ml of dyebath waste water from Dyeing Techniques). 2. Using a pipette, add 5ml of Milton fluid and look for the change in colour. 3. Continue to add 5 ml quantities of the Milton fluid and leave for 5 minutes between each addition to allow it to mix. The children record their observations, including the quantity of Milton's Fluid needed to produce clear water. A typical result would be that a solution of 5ml of blue food colour in 250ml water would need 25ml Milton, added at 5 minute intervals, to remove the colour. Discussion can follow on whether companies might use this or other methods to remove the colour from wastewater (see Background Information). They are unlikely to use anything like Milton's fluid, as they would be adding another chemical to the wastewater that would also need removing before discharging the water from the site. Discharge printing demonstration Discharge printing is a style of decoration often employed in Africa and India, as well as being popular in Western fashion. To demonstrate the technique, cut a simple design into half a potato. Stretch out the fabric over newspaper on a flat surface. Pour Milton's Fluid into the bowl, dip the potato in, and make a repeat pattern of printing on the fabric. The Milton print should produce a white design on the coloured fabric. If the design has irregularities, explain to the children that this is typical of the nature of the technique. Colour changing pens Introduce the children to the colour changing felt pens, which work on the same principle of removing colour and replacing it, or by changing it chemically. Let them experiment with the various combinations of colours and then ask them to produce a design for a repeat pattern which could be used on fabric. A display can be mounted of the children's designs of printed fabrics and clothes.. Background information Stringent environmental regulations govern the discharge of effluent into water systems and the imposition of large fines on companies who do not keep to their agreements make it a very important issue for all companies in the colour industry. Dye waste water can be decolourised by passing it through specially treated, very finely powdered charcoal. The dye is absorbed by the charcoal, leaving a colourless liquid. Companies will need to remove any other chemicals which could harm the environment, using appropriate processes, before discharging the waste water from their site. A characteristic of the discharge printing technique is a lighter coloured design on a dark background. Many examples can be found in fair trade and ethnic charity catalogues, such as Traidcraft, where the most common form is found using indigo as the base colour. A range of fabrics and artefacts from fair trade suppliers can be found on the Traidcraft website on www.traidcraft.co.uk. The technique of discharge printing is also used in some specialised fabric studios for the fashion industry. A more sophisticated version of discharge printing mixes an additional colour with the discharge paste. The paste removes the original colour and substitutes the second colour in one operation. It is not possible to reproduce this in a primary classroom as it requires specialist materials. Extensions / links Art
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