By CraftingStepByStepPublished
Based on a video by Helpful DIY.
Oobleck is cornstarch and water, and that is the whole ingredient list. What makes it worth the five minutes is how it behaves. Squeeze it and it seizes up like a rock. Open your hand and it runs through your fingers like syrup. Kids will stay at the bowl for an hour with it.
Helpful DIY walks through the mix on camera with a small batch, which is the right way to start. You can scale it up once you know what the finished texture should feel like.
Twice as much cornstarch as water, measured by volume. One cup of water needs two cups of cornstarch. A quarter cup of cornstarch needs an eighth of a cup of water.
Hold back a little of the water rather than tipping it all in at once. Adding water to a stiff mix is easy. Pulling it back out of a soupy one means opening the cornstarch again and you can chase that in circles for a while.
Drag a finger across the surface slowly and it should part like a liquid. Tap it fast and it should feel hard. Scoop up a handful, roll it between your palms into a ball, then stop moving. A correct batch holds the ball for a second and then collapses back into the bowl.
| Problem | Fix |
|---|---|
| Runs off your hand, never firms up | Add cornstarch a spoonful at a time |
| Cracks and crumbles, will not flow | Add water a teaspoon at a time |
| Gritty and separating | Keep mixing, it needs another minute |
| Watery layer on top after sitting | Normal, stir it back in |
Cornstarch does not dissolve in water. The grains sit suspended in it. Press down fast and the grains jam against each other with nowhere to go, so the whole thing resists like a solid. Move slowly and the water has time to flow around them and it behaves like a liquid.
The technical name is a non-Newtonian fluid, and it is the same reason cornstarch thickens a sauce on the stove.
Stir it into the water before the water meets the cornstarch. Colour added at the end sits in streaks and takes real work to distribute.
Gel colour gives a deeper shade than liquid drops and adds almost no extra liquid, which matters when your whole water measurement is a few tablespoons. Be aware that a strong colour will tint hands for a few hours and can mark grout and untreated wood.
Do not pour oobleck down the sink. It settles in the trap and sets like concrete. Let the leftovers dry out in the bowl, then it turns back into powder you can tip into the bin and wipe out.
Dried oobleck on clothes and floors brushes off once it is fully dry. Chasing it while wet just spreads it around.
It keeps a couple of days in a sealed container, though it separates and needs a stir. After that it starts to smell and it is cheap enough to just make again.
Cornstarch and food colouring are both food, so a toddler putting a hand in their mouth is not a problem. It is not a snack, but it is not a hazard either. Work over a tray and roll sleeves up.
For more of the same kind of afternoon, try salt dough ornaments or a concrete planter for something that lasts longer.
7 steps · about 6 minutes.Check off each step as you go and your progress saves automatically.
Spoon cornstarch into a bowl. You want twice as much cornstarch as the water you are about to measure, so a quarter cup of cornstarch pairs with an eighth of a cup of water.
Start small on your first batch. It is easier to judge the texture in a little bowl, and cornstarch is cheap enough to make three of them.
Tip
Level the measure off with a knife. Scooped cornstarch packs down and throws the ratio off.
Measure out half as much water as you used cornstarch, into a separate cup. Add food colouring to the water now and stir it through.
Colouring the water first is the difference between an even shade and a streaky one. Once the cornstarch is in there you will not get colour distributed properly without a lot of work.
Tip
Go heavier on the colour than looks right. The white cornstarch will wash it out considerably.
Pour most of the coloured water into the bowl and hold a little back in the cup.
That reserve is your safety margin. If the mix comes out too stiff you have the water right there. If you tip it all in and it goes soupy, you are opening the cornstarch box again and re-balancing the whole thing.
Work it together with your fingers. It resists at first and feels like there is nowhere near enough water, then it turns over into a thick glossy mix quite suddenly.
Mix with one hand and keep the other clean. You will want a dry hand for the cornstarch box, the tap, and anything else you need to reach for.
Tip
Keep going for a full minute before deciding it needs more water. It nearly always comes together.
Push a finger into the surface quickly. It should stop dead, like pressing a worktop. Now rest the same finger on it and let it sink in slowly.
That split behaviour is the test. If fast and slow feel the same, the ratio is off and the table above will tell you which way to correct it.
Add cornstarch a spoonful at a time for a firmer, more solid feel. Add water a teaspoon at a time for something looser that melts faster.
Neither is wrong. Firmer holds a shape long enough to roll a ball, looser is better for pouring and dripping. Let whoever is playing with it pick.
Tip
Adjust in small amounts and mix fully between each. Oobleck takes a few seconds to show what an addition actually did.
Grab a fistful and squeeze hard. It compacts into a solid lump. Open your hand flat and it slumps and runs back into the bowl through your fingers.
Roll it fast between your palms and you get a ball that survives as long as you keep moving. Stop, and it is a puddle. That trick is the whole reason to make the stuff.
Keep going
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