MAKE YOUR OWN S LIME

Focus-Science and Technology - - Diy Science - Dr Stu­art Farrimond is a sci­ence writer, pre­sen­ter and ed­u­ca­tor, and hosts a reg­u­lar seg­ment on BBC Ra­dio Wiltshire. His book The Sci­ence Of Cook­ing is out now.

YOU WILL NEED:

PVA glue Bi­car­bon­ate of soda Con­tact lens so­lu­tion (it must con­tain boric acid) Gel food colour­ing Glit­ter (op­tional)

Ghost­busters made green goop a must-have play­thing more than 30 years ago. Now, slime is all the rage once more. This time, how­ever, it can be made with items eas­ily avail­able in your lo­cal su­per­mar­ket. Slime is great fun to play with, and its prop­er­ties are un­der­pinned by some se­ri­ous sci­ence…

WHAT’S GO­ING ON?

The base in­gre­di­ent for this slime recipe is PVA (polyvinyl ac­etate), which is made up of long, spagetti like mol­e­cules are sur­rounded by water that can slide past one an­other with ease.

The boric acid in the con­tact lens so­lu­tion re­acts with the bi­car­bon­ate of soda to cre­ate sodium tetrab­o­rate. These sodium tetrab­o­rate mol­e­cules form bridges be­tween the PVA strands, pre­vent­ing them from slid­ing past each other so eas­ily. The more boric acid that is mixed in, the stiffer it be­comes, and will grad­u­ally be­come a thick putty. If you get the pro­por­tions right you can achieve some­thing that is a mar­vel­lous half­way house be­tween a free-flow­ing liq­uid and an in­flex­i­ble solid. If it doesn't work first time, keep ex­per­i­ment­ing with the qual­i­ties of the in­gre­di­ents un­til you get mar­vel­lous, gooey slime!

2. Add one tea­spoon of bi­car­bon­ate of soda and thor­oughly mix.

5. Keep mix­ing un­til it starts to come away from the edges of the bowl, then turn out onto a clean work sur­face and knead un­til it reaches the de­sired con­sis­tency.

4. Grad­u­ally add one ta­ble­spoon of con­tact lens so­lu­tion and stir. You may not need all the con­tact lens so­lu­tion, so add slowly and stop when the slime starts to thicken.

3. Add a few drops of food colour­ing, and glit­ter if you like. Stir well.

1. Tip about 200ml of PVA glue into a large mix­ing bowl.

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