How Silly Putty Works

The year was 1949. World War II had been over for four years, and James Wright's bouncing putty was still in circulation as an invention in search of a practical use. Unfortunately, no factory or manufacturing plant ever discovered an application for the goop. Peter Hodgson, who owned his own ad agency in New Haven, Conn., was at a cocktail party when he spotted the putty making the rounds. He watched as people spent minutes at a time folding, stretching and squeezing the strange stuff. He approached Ruth Fallgatter, owner of the Block Shop toy store, about listing the putty in an upcoming catalog Hodgson was helping to produce. Fallgatter agreed, and the two decided to list it on a page with other adult gifts for the price of $1 [source: Miller].

The bouncing putty became one of the Block Shop's biggest sellers. For reasons that remain unclear, Fallgatter declined to market the product any further, but Hodgson saw its potential. He borrowed $147 to order another batch from General Electric, then hired a Yale student to place 1-ounce (28-gram) wads in plastic eggs. At the same time, Hodgson began to brainstorm names for his product. He evaluated 15 possibilities, but eventually settled on Silly Putty, for which he secured a trademark. Next, he established Arnold Clark Inc. to sell the stuff and contracted with some chemical engineers in Schenectady, N.Y., to derive a recipe based on General Electric's original formula. Hodgson opened a manufacturing plant in North Branford, Conn., to make Silly Putty and, soon after, landed his first customers -- Neiman Marcus and the Doubleday bookshops [source: Crayola].

Then, in August 1950, The New Yorker featured Silly Putty in its Talk of the Town section:

With that endorsement in The New Yorker, interest in Silly Putty skyrocketed. Arnold Clark received more than a quarter-million orders in three days, and Hodgson's great gamble had paid off. The soft, malleable material soon became a fixture in homes across North America and eventually -- the world. When Hodgson passed away in 1976, Silly Putty was being sold throughout the United States and 22 other countries, with annual sales exceeding $5 million [sources: Haynes, McFadden].

Today, Silly Putty continues to amuse and entertain. Up next, we'll take a closer look at its unusual properties and how they can lead to a contradiction in terms.

The original Silly Putty didn't look very exciting. It arrived in an egg and fell out of its shell like a pink blob. The egg had no significance except that Peter Hodgson began selling his product in the weeks leading up to the Easter holiday. It even came delivered in dozen-pack cardboard egg cartons. But the egg quickly became part of Silly Putty's brand, and Hodgson decided to keep the unique packaging long after the first Easter selling season had come and gone.

When you removed the putty from the egg and began to handle it, you saw its peculiar properties immediately: It stretched like taffy, yet broke into pieces if you struck it sharply. You could form it into shapes, like Play-Doh, but unlike its modeling-compound cousin, which held a pose indefinitely, Silly Putty flowed in slow motion. Stick it on the side of a filing cabinet, for example, and it would run down the side slowly, taking weeks -- even months -- to respond to gravity's downward pull. Roll it into a ball and throw it at the ground, and it would bounce 25 percent higher than rubber [source: National Toy Hall of Fame].

In early marketing efforts, Hodgson summed up Silly Putty's enigmatic properties by describing the material as a "solid liquid" [source: Crayola]. Interestingly, he didn't think these qualities would attract kids. In fact, Hodgson saw his product as a purely adult diversion.

"It means five minutes of escape from neurosis," he said in the 1950 article for The New Yorker. "It means not having to worry about Korea or family difficulties. And it appeals to people of superior intellect; the inherent ridiculousness of the material acts as an emotional release to hard-pressed adults."

The official patent document echoed this sentiment by proposing the following practical uses: relieving stress by enabling patients in need of hand therapy to squeeze and manipulate the putty; making impressions of newsprint to relieve boredom; cleaning typewriter keys; blocking low-frequency sounds and sealing vacuum joints.

It didn't take long for kids to see what adults were playing with and to sneak some covert samples. And luckily for everyone, one of Silly Putty's other properties -- nontoxicity -- meant that no one had to worry about accidental poisoning. By 1955, the market flipped, and Silly Putty sales to children overtook sales to adults [source: Crayola]. Eventually, chemistry teachers began to take notice and started teaching the science of Silly Putty. We'll cover some of that science in the next section.

To understand how Silly Putty works, you have to take a dive into the concept of fluid chemistry. You probably think of water when you hear the word fluid, but to chemists and physicists, a fluid is any substance that has no fixed shape and yields easily to external pressure. By this definition, gases can be fluids, as can certain solid-type materials.

A key property of fluids is something known as viscosity, which measures how much a fluid resists flow at a certain temperature. Molten glass, for example, has a high viscosity, or resistance to flow. Other viscous materials include honey, molasses and engine oil. Water, on the other hand, has a lower viscosity. Here are their viscosities at temperature of 68 degrees F (20 degrees C). Note that the measurements are given in pascal seconds, the standard unit of viscosity in the International System of Units.

As you know from experience, viscosity varies with temperature. It's why honey and syrup flow more easily when heated and why engine oils and hydraulic fluids perform poorly on really cold days. This is true for most fluids -- their viscosity depends only on temperature. Chemists classify such materials as Newtonian fluids in honor of Isaac Newton, who pictured a fluid as a series of layers sliding past each other and reasoned that viscosity is the result of friction between these layers.

Silly Putty is non-Newtonian fluid: Its viscosity depends on both temperature and on the force applied to it. The classic example of such a fluid is corn starch solution. When you mix water with corn starch, you get a material that feels like a thick fluid when it's stirred slowly. Tap on it, though, and it feels like a dense solid. Pour some of the corn starch mixture into your hand and roll it gently, and it will maintain its ball shape. Stop rolling it, and it forms a puddle in the palm of your hand. In other words, it acts like a solid and a liquid all at once.

It seems Peter Hodgson was correct when he described his invention as a "solid liquid." Unlike corn starch solution, however, Silly Putty's solid nature resembles rubber, not rock. That's because its main ingredient is polydimethylsiloxane, a material with viscoelastic properties. In other words, over long flow times or at high temperatures, Silly Putty behaves like a highly viscous fluid. But over short flow times or at low temperatures, it behaves like an elastic solid.

You don't have to have a degree in chemistry or a complex factory to make Silly Putty. A homemade version requires some readily available ingredients and just a few minutes of experimentation. Your course in kitchen chemistry begins on the next page.

Teachers love Silly Putty because it embodies the spirit of hands-on science -- and because it offers a fun way to demonstrate how polymers, or long chains of molecules repeated over and over again, work. But buying putty-filled eggs for an entire classroom can be cost-prohibitive. Luckily, it's not too hard to whip up a little private label Silly Putty using ingredients you can find around the house or at the drugstore. The most common recipe uses the following:

No chemistry experiment is complete without some equipment. You'll need measuring spoons and a measuring cup to get the right proportions for the mixture. You'll also need a large bowl, a small plastic cup and a spoon to mix ingredients together. You might also have a resealable plastic bag or container on hand if you want to save your homemade putty for a few days.

Once you have all of your supplies, you're ready to get silly. Just follow these steps, and you'll be playing with putty in no time:

This concoction will undoubtedly impress your friends, but they'll be even more impressed if they hear you explain the chemistry. Here's what's happening: Glue contains a polymer called polyvinyl alcohol, or PVA. In the glue-water mixture, these polymer chains slip and slide past each other easily. But when you add the borax solution to the glue, it connects one PVA molecule to another in a process known as cross-linking. As more chains link up, they no longer slip and slide. Instead, they form a large mat that resembles a net or a spider's web. This is what gives the material its puttylike qualities.

Of course, nothing beats the original Silly Putty you can buy at the toy store. Snap up more links to classic toy tidbits next.