Cornstarch Goop: Wet and Dry and Wet Again

 After the explorations with frozen goop, I let the goop dry in the sensory table, and then gave the children the ingredients to mix a new batch of goop.

There’s no recipe, just cornstarch and water. I added liquid watercolor paint to the water, and placed the pitchers of water and bowls of cornstarch in the sensory table for the children to discover.

At the end of the day, it was time to leave the goop to dry out again. By the next day, it had dried into a thick, chalklike sheet, which crumbled easily into large and small pieces that could be scooped and spooned.

But, what is dry can be made wet again, so it was time for more pitchers of colored water.

Once everything was mixed together, it was too watery, so it I refilled the bowls of cornstarch.

And, once more, the mixture dried out again. All ready to be made wet again the next day.

Note: If you want to try this yourself, here are some tips. 1) If the goop is very wet at the end of the day, drain off excess water before leaving it to dry. 2) Be sure to leave the sensory table uncovered. If you have to cover it, use a light sheet and leave it vented on the sides so air can get through. 3) The drying process doesn’t work as well in humid weather. 4) If your goop starts to smell bad, or has black specks in it, it’s time to throw it out, sanitize the sensory table, and start again with a new batch.

Frozen Goop

I’ve written before about cornstarch goop (aka “oobleck”). It’s a mixture of cornstarch and water that changes state from solid to liquid as you stir it, pick it up, or press it in your hands.

Another way to use this material is to freeze it. Frozen goop is truly a mystery material. Children don’t have any prior knowledge or experience to base their actions on, so they approach this material with curiosity and scientific exploration.

I prepared the goop by mixing cornstarch and water, then pouring it into small plastic cups with some liquid water color paint. I put the cups in the freezer overnight. Getting the frozen goop out of the cups is tricky – you have to let them defrost a little bit first. I put the cups on the heater vents, but you could also dip them in warm water to loosen the goop from the cup.

Once I got the goop out of the cups, I put it into the sensory table with some various small cups and scoops.

It looked a little like ice cream, even though after touching it, no one seemed interested in putting it in their mouths.

The texture was something like very cold, icy snow. As it warmed, it melted into a thick, syrupy goop that slid on hands and across the table, and that could be spooned and scooped, and poured from cup to cup.

Gluten Free Playdough

One of the basic staples in my classroom is playdough. I almost always have playdough, or a similar material available daily. I use a homemade cooked playdough recipe (more about that here), that’s flour based. One the downsides of homemade and many store bought playdoughs is that because of the flour, children who are gluten free or have a wheat allergy can’t use it, and in an allergen aware classroom, it might not be allowed.

So I tried out some different dough recipes that didn’t use flour. Many of them made different goop concoctions, which can be rich sensory activities, but they don’t have the same properties as playdough. Finally I found this one – a cooked recipe of cornstarch and baking soda. Even if you don’t have any restrictions that keep you from using a flour based dough, it’s nice to provide the children with materials that have various textures. This dough is slightly softer than traditional flour-based playdough, and feels cooler to the touch (similar to cornstarch goop), but holds up just as well during play and has a similar shelf life.

Here’s the recipe:

1 cup cornstarch

2 cups baking soda

1-1/4 cups cold water

1 tablespoon vegetable oil

1 tablespoon food coloring

  

Mix all ingredients together over low heat until the dry ingredients all dissolve.

 Keep stirring for about 5 minutes until it starts to bubble.

Once it bubbles, it will start to thicken slowly. Keep stirring for another 2 or 3 minutes.

If you’ve ever made cornstarch goop, the mixture will have the same properties as it cooks, looking solid, then turning liquid when you try to pick it up.

Soon it will start to solidify. It will look like mashed potatoes or grits.

 When it turns solid and starts forming a ball, take it off the heat and let it cool. Store in a sealed container.

 

Cornstarch Goop

Cornstarch goop (aka 'Oobleck") is a perfect medium for scientific exploration. There are only two ingredients – cornstarch and water. As the children mix it together, its properties and texture change, providing opportunities to observe and figure out what has happened, and what might happen next.

I set up the activity on individual trays, so each child can have control over their own exploration process from beginning to end. There’s no exact “recipe”, but I start with giving each child an equal amount of water and cornstarch. They can decide if they need more.

Adding color extends the activity by giving more dimensions to observe and interact with. The color also makes it easier to see the physical changes in the mixture, since the color mixes with the more liquid part of the mixture, floating above the solid goop. I used liquid watercolor, which doesn’t stain the way food coloring can.

 The goop is also a medium for studying color mixtures. Diffused through the thin cornstarch mixture, the colors swirl and combine slowly, allowing the children to control the combinations, and observe the effects of their actions.