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Sophie Duncan sticks to the point

Science Corner this week explores the sticky world of glue. You can make your own, using flour or milk, and test its adhesiveness.

Glue was first patented in 1750 and was initially made from fish. Other patents followed that used animal bones, starch, rubber and casein, a by-product of milk.

Milk is a great basis for glue. Take half a cup of milk and mix it with a tablespoon of vinegar. Heat gently and stir. As the mixture warms, lumps of casein will form. Carry on stirring until the lumps have stopped forming, and then strain out the casein using a muslin bag.

Put it into a jar and add a tablespoon of water and a quarter of a tablespoon of baking soda to form a white glue; if it is too thick add more water; if too lumpy add more baking soda.

Alternatively, after straining the casein, squeeze it through the muslin into a clean jar, then let the casein dry into a powder. Add a small amount of borax and water to make the powder into glue.

You can also make glue from flour and water: try using two parts flour to one of water. Heat the mixture until it boils if you want to strengthen it.

Testing glue is great fun. Indeed, the scientist who invented Post-it Notes was experimenting with glue when he realised he had created something new.

In order to test your glue you need a fair test. Here are some suggestions:

* Stick a bottle-top to a piece of card with a measured amount of glue, turn it upside down and time how long it stays stuck.

* Stick an envelope to a piece of upright card by its flap. Add pennies to the envelope until the glue gives.

Does length of drying time affect the result?

Sophie Duncan is project manager for science at the BBC

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