How to Make Kinetic Sand

Set a wide plastic bin on a drop cloth or take the whole job outside. Scoop five level cups of dry play sand into it with a one cup measure, counting out loud as you go so you do not lose your place. Level the top of each cup off with your finger.

Play sand from the hardware store is the right kind. It is washed and sifted for sandboxes, so it pours clean and does not carry the grit and shell fragments you get from a beach.

Measure three cups of cornstarch and tip them straight onto the sand in one pile in the middle. Keeping it in a heap rather than scattering it lets you see at a glance how much has gone in.

Cornstarch is what turns loose grains into sand that sticks to itself, so the five to three ratio is worth getting right. Scrape the measure level each time. A cup packed down heavy throws the whole batch off.

Put both hands in and turn the two together. Rake your fingers along the bottom of the bin and lift, rather than stirring across the surface, because the cornstarch sinks and hides down there.

Keep going until the white streaks are gone and the whole bin reads as one even grey. Then push the mix out toward the sides to leave a shallow well in the middle, the way you would for bread dough.

Fill a one cup measure with cooking oil and pour it into the well. Olive, vegetable, canola, whatever is open in the cupboard. The oil is doing a mechanical job, not a chemical one, so the type does not change the result.

Pouring into the well instead of across the top keeps the oil in one pool. That matters more than it sounds, because chasing a spreading slick of oil around a wide bin is the fiddly part of this whole thing.

Pull the dry mix in over the oil and start rubbing handfuls between your palms. For the first minute it looks wrong, wet in one place and powdery an inch away, and that is exactly what it should look like.

Hunt down the shiny patches and bury them under dry sand from the edges. Squeeze, release, squeeze again. Every squeeze pushes oil into grains that have not been coated yet.

Work the whole bin, corner to corner. Lift from underneath and let the mix fall back through your fingers so you can see what is in there. Pale crumbs that puff into dust are cornstarch that never met the oil.

Fold those dry pockets toward the damper sand rather than reaching for the oil bottle. There is enough oil in the bin already. It has not travelled yet.

Flatten the surface with your palms and lean on it. Finished kinetic sand takes the print of your hand and keeps a clean edge, and a fistful squeezed and opened stays in one lump instead of falling apart.

Crumbly means it needs more mixing, so put your hands back in for another minute. Greasy or slick means work in a few spoonfuls of cornstarch, a little at a time, until it stops shining.

Push an upturned cup or a sand mold down into the packed surface, give it a small twist, then lift it straight up. A dome should stand there on its own. Build three or four in a row across the bin.

Then slice them apart with the edge of your hand and watch the sand fall in that slow, heavy way. Squash it all flat and do it again. Spoons, cookie cutters and beach molds all work.