The Spark2 Giant Bubble
— recipe, wand & the science behind it.

How to run it

1. Cut the bottom off a plastic bottle. Stretch the toe of an old sock over the cut end and secure with the elastic band.
2. Mix a saucer of washing-up liquid with a few tablespoons of water.
3. Dip the sock end into the mixture. Then blow gently into the open neck of the bottle.
4. A long "snake" of foam bubbles will pour out the sock end. Children can blow snakes a metre long.

What they'll wonder

Why are there hundreds of small bubbles instead of one big one? (The sock has lots of tiny holes, so each bubble forms separately.) Can you make a longer snake by blowing harder? (Try it. It changes shape but not length.)

The stronger recipe — glycerin is the secret

This experiment works ten times better with glycerin in the mix. Glycerin (sometimes labelled glycerol) is what stops the water in the soap film evaporating — bubbles get strong enough to nest, poke and even bounce. Most chemists, supermarkets and Amazon sell it for a few pounds.

How to run the experiment

1. Pour a thin layer of the glycerin mixture across the tray.
2. Wet the end of the straw in the mix, then blow gently against the tray surface. A dome-shaped bubble forms.
3. Now wet a child's finger in the bubble mix. Push it through the side of the dome — it doesn't pop.
4. Push the wet straw through the dome and blow another bubble inside the first. With glycerin in the mix you can nest four or five bubbles inside each other.

Bonus: bouncing bubbles (extension)

Same glycerin mix, no straw needed. Each child holds a wool scarf or fluffy mitten flat across both palms. Blow a small bubble in the air, then catch it gently on the wool surface. With glycerin in the mix and a dry-wool surface, the bubble bounces instead of popping. Children can pass it from hand to hand like a delicate ball. The science is the same as the wet-finger trick — wool fibres are dry but rough enough that the soap film never fully contacts a smooth surface, so it doesn't break.

What they'll wonder

Why does the wet straw not pop the bubble, but a dry one would? Why does adding one extra ingredient change everything? Cue the science: anything wet with bubble mix slides through the film without breaking it. Anything dry breaks the film — unless the surface is so dry-and-fluffy that no smooth contact happens at all (the wool trick).

How to run it

Make four versions of the bubble mixture. Each one changes one variable — that's the fair-test rule. Children predict, test, and record.

1. Mixture A: the standard recipe (control)
2. Mixture B: double Fairy Liquid (10 tbsp)
3. Mixture C: half cornflour (1 tbsp)
4. Mixture D: add 1 tbsp glycerine (the secret weapon — most chemists sell it)

What to measure

• Bubble lifetime: stopwatch from leaving the wand to popping. Average 3 attempts.
• Bubble size: measure with arms — small / medium / large / very large.
• Children's vote: which mixture made the prettiest bubbles? Easiest to make? Strongest?

What they'll discover

Glycerine wins on lifetime — it slows water evaporation. Doubled Fairy Liquid actually weakens bubbles because too many soap molecules stop the film holding together. Half cornflour = thinner bubbles that pop fast.

The lesson isn't the result — it's that science is about changing one thing at a time and measuring. Post-SATs gold.