There was a time when taking a perfect shot in a game of billiards could cause the ball to explode.

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That’s because the balls were made of celluloid, an early plastic that was, unfortunately, combustible. It was patented on this day in 1869, just a few years after the first human-made plastic, Parkesine.

Although it later came to be associated with film (where its combustibility was also famously an issue), celluloid, like many other early plastics, originated as part of an attempt to solve a non-mathematical billiards problem: the ivory problem.

In the mid-nineteenth century, writes Lauren Davis for iO9, “there was a common, although erroneous, belief that ivory was in short supply.” At the same time, according to Roman Mars on the podcast 99% Invisible, billiards was extremely popular.

It was the huge popularity of billiards, combined with this fear of a dwindling ivory supply, that led to the development of plastic, a material that “came to define the modern world,” says Mars.

“The billiard ball has to have certain physical properties. It has to rebound properly. It has to be of a certain density,” one billiards expert explained to Mars. The only material that would do everything the game required was top-grade ivory, which according to Mars “was actually called billiard-ball ivory.”

In the search for a substitute to this expensive and difficult-to-obtain material, a major company that made billiards supplies, Phelan and Collender, offered a $10,000 reward (several hundred thousand dollars in today’s money) to anybody who could invent one.

Although Alexander Parkes managed to produce the first material that approximated ivory, Parkesine was didn’t lend itself to commercial-scale manufacture. Celluloid, developed by John Wesley Hyatt, did.

“Celluloid and its predecessors were all made with nitrocellulose, also known as pyroxylin, flash paper and gun cotton,” Davis writes. “As you might guess from that string of names, these plastics were highly flammable, and when used in billiard balls, they had some, well, interesting results.”

Occasionally, as Hyatt himself recalled, two balls hitting each other would produce “a mild explosion like a percussion guncap.”

“We had a letter from a billiard saloon proprietor in Colorado, mentioning this fact and saying that he did not care so much about it, but that instantly every man in the room pulled his gun.”

This cavalier attitude to personal safety also showed up with other celluloid products. Besides billiard balls, celluloid was used to make lady’s combs and other fashion products like buttons, collars and dentures. The material’s easy flammability was a problem in all those places, too, writes Ria Misra for i09.

Today, billiard balls are made out of resin, and elephant numbers are in decline due to poachers seeking ivory—now a banned substance.