Silly Putty History and Chemistry

Science of Toys

Silly Putty has properties of a liquid and a solid.
Silly Putty has properties of a liquid and a solid. Eric Skiff

Silly Putty History

James Wright, an engineer at General Electric's New Haven laboratory, may have invented silly putty in 1943 when he accidentally dropped boric acid into silicone oil. Dr. Earl Warrick, of the Dow Corning Corporation, also developed a bouncing silicone putty in 1943. Both GE and Dow Corning were trying to make an inexpensive synthetic rubber to support the war effort. The material resulting from the mixture of boric acid and silicone stretched and bounced farther than rubber, even at extreme temperatures.

As an added bonus, the putty copied newspaper or comic-book print.

An unemployed copywriter named Peter Hodgson saw the putty at toy store, where it was being marketed for adults as a novelty item. Hodgson bought the production rights from GE and renamed the polymer Silly Putty. He packaged it in plastic eggs because Easter was on the way and introduced it at the International Toy Fair in New York in February of 1950. Silly Putty was a lot of fun to play with, but practical applications for the product weren't found until after it became a popular toy.

How Silly Putty Works

Silly Putty is a viscoelastic liquid or non-Newtonian fluid. It acts primarily as a viscous liquid, though it can have properties of an elastic solid, too. Silly Putty is primarily polydimethylsiloxane (PDMS). There are covalent bonds within the polymer, but hydrogen bonds between the molecules. The hydrogen bonds can be readily broken.

When small amounts of stress are slowly applied to the putty, only a few of the bonds are broken. Under these condition, the putty flows. When more stress is applied quickly, many bonds are broken, causing the putty to tear.

Let's Make Silly Putty!

Silly Putty is a patented invention, so specifics are a trade secret. One way to make the polymer is by reacting dimethyldichlorosilane in diethyl ether with water. The ether solution of the silicone oil is washed with an aqueous sodium bicarbonate solution. The ether is evaporated off. Powdered boric oxide is added to the oil and heated to make the putty. These are chemicals the average person doesn't want to mess with, plus the initial reaction can be violent.

There are safe and easy alternatives, though, that you can make with common household ingredients:

Silly Putty Recipe #1

  • solution of 55% Elmer's glue solution in water
  • solution of 16% sodium borate (Borax) in water
  • food coloring (optional)
  • Ziploc bags

Mix together 4 parts of the glue solution with one part of the borax solution. Add food coloring, if desired. Refrigerate the mixture in the sealed bag when not in use.

Silly Putty Recipe #2

  • 2 parts Elmers' white glue
  • 1 part liquid starch

Gradually mix the starch into the glue. More starch may be added if the mixture seems too sticky. Food coloring may be added, if desired. Cover and refrigerate the putty when not in use. This putty can be pulled, twisted, or cut with scissors.

Explore the interesting properties of Silly Putty.

Silly putty bounces like a rubber ball (except higher), will break from a sharp blow, can be stretched, and will melt into a puddle after a length of time. If you flatten it and press it over comic book or some newpaper print, it will copy the image.

Bouncing Silly Putty

If you shape Silly Putty into a ball and bounce it off a hard, smooth surface it will bounce higher than a rubber ball. Cooling the putty improves its bounce.

Try putting the putty in the freezer for an hour. How does it compare with warm putty? Silly Putty can have a rebound of 80%, meaning it can bounce back to 80% of the height from which it was dropped.

Floating Silly Putty

The specific gravity of Silly Putty is 1.14. This means it is more dense than water and would be expected to sink. However, you can cause Silly Putty to float. Silly Putty in its plastic egg will float. Silly putty shaped like a boat will float on the surface of water. If you roll Silly Putty into tiny spheres, you can float them by dropping them into a glass of water into which you have added a little vinegar and baking soda. The reaction produces bubbles of carbon dioxide gas, which will stick to the spheres of putty and cause them to float. As the gas bubbles fall off, the putty will sink.

The Solid Liquid

You can mold Silly Putty into a solid form. If you chill the putty, it will hold its shape longer.

However, Silly Putty isn't really a solid. Gravity will take its toll, so any masterpiece you sculpt with Silly Putty will slowly soften and run. Try sticking a glob of Silly Putty to the side of your refrigerator. It will stay as a glob, showing your fingerprints. Eventually it will start to ooze down the side of the refrigerator.

There is a limit to this -- it won't run like a drop of water. However, Silly Putty flows.