Hair may seem an unconventional material to choose for scientific investigations at key stages 2 and 3. It is, of course, a renewable resource. You may not be keen to make a hair shirt, or to stuff a mattress with it, but it provides an unusual raw material for study.
Obtaining a range of hair samples to test needs some care, since your students may have litigious parents. Even when confronted by a room bursting with Pre-Raphaelite luxuriance, teachers should be sure to ask permission in advance.
Elastic hair and Hooke's Law
Most students will have investigated the stretchiness of springs. It is more fun testing your own hair.
Use a single hair, secured to the end of a metre rule. Attach a paper clip to the loose end of the hair and add 10g weights, one at a time. Record the hair's length each time and the mass added. Watch out for the elastic limit. When you stretch hair too much, it will not return to its original length once the weights are removed. It is then beyond the elastic limit.
Extend this investigation by soaking the hair in water first or by steaming it in front of a kettle. Wet hair will stretch further but it is likely to break more easily. There will be lots of opportunities here for display work and the use of graphs and data charts.
The acid test for conditioning
Many hair products contain acids. Hair can be made smoother by treatment with a weak acid.
Use small bunches of hair for this test. Keep one dry for comparison and soak the other samples in weak acids such as vinegar or citric acid, or even lemon juice. Include one alkali for contrast, say ammonia solution or washing soda. After 45 minutes rinse the samples. The acid soaking should make the hair feel smoother. The alkali will have the opposite effect, the hair will swell and feel rougher. Try a commercial conditioning product and compare the results. It is also worth investigating the effects of household soap solutions. Soaps are generally alkaline.
Colour it now
If you add hair colour to natural hair, the new colour will simply modify the existing colour. Some bizarre and unpredictable effects can be produced this way. One alternative is to remove the original colour by bleaching before adding the new hair dye.
There are many kinds of bleach that children can investigate, for example hydrogen peroxide. This material has been used as a bleach, to clean contact lenses and false teeth and, at high strength, as a rocket fuel.
The peroxide breaks down to release oxygen and this is a good place to start.
Show that hydrogen peroxide releases oxygen gas like this. Take a small sample in a tube and add a slice of raw potato. The tube soon fills with an oxygen-rich foam. Many commercial hair bleaches have two components which are mixed before use. In addition to the peroxide, the second material is an alkali such as ammonium carbonate. This was used as an ingredient in sal volatile, or smelling salts, used to revive someone after they fainted.
Testing bleach on hair
Use small bunches of hair for the bleach tests. Try different proportions of peroxide to ammonia solution, starting with 10:1 of ammonia. Ammonia solution needs to be handled with care in a well- ventilated place.
Hair bleaches are designed to work best at body temperature, about 37 LESS THAN C. Use an insulated plastic coffee cup to keep the bleach warm. Rinse and dry the bleached samples and use them in a display.
Adding the new colour
Use a natural dye such as henna with the bleached hair samples. Henna has been used to dye the tails and manes of horses. If you can obtain some horse hair, try this as well. Henna gives hair a red-brown colour and can also be used to dye elaborate patterns directly on to the skin.
Soak the bleached hair sample in a solution containing henna. Try a range of times and temperatures to produce different colour intensities. The dyed samples may continue to change colour for several days when left exposed to the air. As an extension activity, try adding both bleaching agent and dye at the same time. See if the colours are better.
Getting the colourright inside
No hair dye lasts forever. It may fade or wash out or be spoiled by new hair growth underneath. The so-called permanent dyes last longer because the colour is absorbed inside the individual hairs. Children can investigate what kinds of materials prevent a dye getting inside.
Use sticks of white blackboard chalk to represent the separate hairs. Try coating chalk sticks in a range of materials such as hair lacquer, petroleum jelly or hair oil. Place the chalks in contact with some blue ink and see how quickly the colour is absorbed.
Finding the best way to dry hair gives a new slant to the study of evaporation.
Use wet hair samples with a range of drying methods. Try hair dryers on hot and cold settings and the heat from light bulbs or infra-red heaters. Ask the children to consider why some heat sources are never used (or not more than once); for example, gas flames.
Heat some dry hair in a tube, look for evidence of carbon (black) and the characteristic smell of ammonia.
* Compare the strength of 10 long hairs, both as separate strands and when plaited together.
* Research the use of macassar hair oil and the use of antimacassars on chairs in Victorian households.
* Compare the effectiveness of soaps and shampoos in cleaning greasy hair.
* Design an experiment to find if dry hair absorbs moisture from the air.
Science at the hairdressers is relevant to lessons with the following key stage objectives:
* Science at KS2 and KS3 properties of materials
* Technology at KS2 and KS3 products and uses of materials.
Risk assessments must be carried out before doing practical work with children.
Hydrogen peroxide - oxygen bleach, former rocket fuel and origin of the term "peroxide blonde".
Bleach - a material that takes the colour from a substance.
Elasticity - a measure of the ability of a material to return to its original size after stretching.
Hooke's Law - the extension of a spring is proportional to the load added.
Pigment - material used to give colour.
Ray Oliver is a former teacher and freelance writer