Stay-at-home science project: Two-ingredient Silly Putty
Easy peasy, putty squeezy.
Welcome to PopSci’s at-home science projects series. On weekdays at noon, we’ll be posting new projects that use ingredients you can buy at the grocery store. Show us how it went by tagging your project on social media using #popsciprojects.
Silly Putty is a toy most anyone can appreciate. Pinch it, bounce it, stretch it, slap it on the side of your face—it does whatever you want it to do, with little complaint.
But the chemical properties that make Silly Putty so bendy and durable are shockingly complex, as are its ingredients. The list is long and includes tongue twister-like names like polydimethylsiloxane and boric acid. Sounds tough to replicate at home. Or is it?
This experiment lets you turn two common goods (cornstarch and dish soap) into endless hours of non-Newtonian fun.
- Time: 5 minutes
- Difficult: easy
What you’ll need
- ⅔ cup of cornstarch
- ½ cup of dish soap
- Small container or bowl
- Food dye (optional)
1. Pour the cornstarch and dish soap into a container. Add a few drops of water to help the goop bind, then fold it all together with a spoon.
- Note: Your putty will have a slight hint of color if you choose dish soap that’s green, yellow, or another hue.
2. Mold the putty with your hands until most of the starch and soap is used up. If the mixture is too dry and crumbly, squeeze in some extra soap. If the mixture is too liquid, sprinkle in some more starch.
3. Play with it. When you’re done, store it in a cool, dark place until you’re ready to mess with it again.
How it works
In terms of chemistry, dish soap and cornstarch are perfect partners; they’re like a couple that hits it off after the first blind date. Dish soap is a surfactant, meaning its molecules have polar opposite ends—a positively charged head and a negatively charged tail. This causes it to stick to compounds such as oil and link up with the long carbon chains found in cornstarch, says Keisha Walters, a polymers scientist at the University of Oklahoma. (Flour, she explains, is way more processed, so if you substitute it for starch in this experiment, the putty will fall apart.) With a little water to help fire up the bonding process, the soap and starch form a sometimes-liquid, sometimes-solid that consistently snaps back to its shape.
Besides dish soap, surfactants are found in a number of things you eat, drink, and put on your body. “They help us stabilize orange juices and non-dairy milks so that the foods don’t separate into liquids and gross oils,” Walters says.” They’re in our ice cream and condiments, and our cosmetics and toothpaste.”
If you’re still scratching your head over this chemical reaction, Walters suggests testing out some other non-toxic mixtures. “The understanding deepens as you play more.” So go ahead—try as many twists on Silly Putty as you want. It was made to stretch your imagination anyway.