Plug into plant power
Making vegetable clocks, onion-coloured T-shirts and conker soap are just some of the activities Ray Oliver describes
Fruit and plant material provide an unusual, and sometimes edible, focus for explorations. These natural materials allow us to extract dyes for a design and make assignment in technology, or produce soap from seaweed or even turn an orange into a battery. Connecting several cells together gives a fruit battery. Oranges and lemons contain a solution of citric acid. In lemons, the acid concentration is high enough to give the characteristic sharp taste. Cut the fruit into thick slices and push two different metals into each slice. Chemical reactions between the metals and the acid in the fruit juice cause electrons to flow along the wire: an electric current. The investigation can use a range of fruit and vegetables - potatoes work quite well. Pupils can consider the drawbacks of fruit batteries. For example, the voltage is unstable, the metals corrode and the battery stops working if the fruit dries out.
Citric acid from a lemon There is enough citric acid in lemon juice to form crystals. The coloured impurities can be absorbed by charcoal dust. They stick to the surface and can then be separated. Squeeze the juice from a lemon and dilute 1:1 with water. Filter the hot mixture and leave the solution of citric acid to evaporate and cool, leaving colourless crystals. Dilute some fresh lemon juice with water in various ratios such as 1:10, 1:50 and 1:100. Fruit to dye for In technology, work on textiles usually includes practical work on finishing techniques in a design and make activity. Fruit and other plant materials are the source of many natural dyes for textiles. Dyes can be extracted and then applied to fabrics to investigate a range of colour effects, colour fastness and resistance to fading in daylight. Examples include tea-leaves, club mosses, rhubarb leaves, lemon juice and alum.
Pupils could compare mordants, say alum and rhubarb leaves. The key chemical in rhubarb leaves is the poisonous acid, oxalic acid (ethanedioic acid). For alum, use a mordant solution of 10g in 100ml of water. For rhubarb, boil the chopped leaves in water for an hour and strain the mordant solution. The fabric samples can be strips of cotton or lengths of wool. The samples need to be boiled in the mordant solution (10-40 minutes) and rinsed before applying the natural dye. Choosing the dye Various roots and leaves will make dyes. To prepare natural dyes, follow these steps:
Suggestions
Plant Mordant Colour
Blackcurrant Alum Violet/purple
Redcurrant Alum Red-brown
Onion skins (boil) Alum Orange
Plum Alum Yellow/pink
Sunflower Alum Yellow
Logwood Alum + washing soda Purple
Applying the dye
The cotton or wool strips can be soaked in the cold dye solution or boiled. If the dyed fabric is part of a focused practical task it will be important to test the colour fastness. Try cutting a sample into four pieces. Soaps and shampoos improve the "wettability" of surfaces by lowering the surface tension of water.
Alkali from the ashes People have been preparing soaps from plant material for hundreds of years. Traditionally, burning plants such as barilla (Salsola sativa) gave an ash rich in alkali. Simply stir the ash with water, filter and test with an indicator.
Soap-making Safety glasses essential. This crude soap will contain some sodium hydroxide. The alkali sodium hydroxide works well in soap-making. Sounds promising.
* Mix 15ml olive oil with 50ml dilute sodium hydroxide solution in a beaker * Cover with a watch glass to reduce loss of liquid * Boil and then simmer for about 30 minutes * Cool. * Test the gelatinous soap for its ability to make a lather with water.
Horse chestnut soap The fruit of Hippocastanaceae, the horse chestnut or conker, has medicinal uses documented as far back as the 16th century. Conkers contain saponins, chemicals which form lathers when shaken with water. * Cut off the brown outer layer * Chop the inner part of the fruit into small pieces * Cover with water in a beaker and boil for 10 minutes * Cool. Filter the mixture * Shake a sample of the solution with water to give a long-lasting lather. Compare with the lathers produced by commercial soaps.
The hair story Most textiles are woven from fibres. Human hair is a widely available renewable resource but little used, even for the penitent's hair shirt. The technology and science of hair provides opportunities for investigations.
Strength and stretch of hair:
Add weights until the hair snaps. A single hair should support 70g-90g.
Shampoo magic and myth Many commercial shampoos feature natural ingredients, fruit extracts and oils designed to improve the hair. Using a group of hairs from one source, investigate the effect of a shampoo on the strength of the hair.
* Soak a bundle of hairs in a small amount of the chosen shampoo.
* Repeat the strength test (above) using wet and dry hair samples.
Alkalis have pH values above pH 7, neutral. Such shampoos claim to provide the best conditions for cleaning hair. Neutral water has a pH of 7. Try the effects of lowering the pH (more acidic conditions) on hair strength.
* Soak the hair sample in an acid such as citric acid or orange juice.
* Test the wet strength of the hair. If the sample is rinsed in water (pH7) the pH will rise towards neutrality. Pupils may conclude that pH-balanced shampoos are less beneficial than they once thought.
The Craft of Natural Dyeing - Glowing Colours from the Plant World by Jenny Dean (Search Press)
Your Yarn Dyeing by Elsie Davenport (Select Books)
The Right Chemistry?
Post a Comment