Where do Ping Pong balls come from?

Hey, Elf Master:

I have a couple of questions for you about Ping Pong balls: what are they made of and how are they made? I know there are more profound questions I could ask, but I am bored and have already taken the phone apart twice.

-- M. Dudley, out there

While you were wantonly destroying household appliances, the elves were in their lederhosen and funny hats, yodeling their way through Germany in search of Joachim Kuhn. He's the physicist in charge of balls for the International Table Tennis Association (called the ITTF, for some reason). Herr Kuhn was happy to answer your questions. I mean, how often does a physicist in charge of Ping Pong balls get interview requests.

Table tennis balls are made of celluloid. Always have been. They've tried other materials, but none is resilient enough to take the punishment of being whapped around by professionals. All the world's table tennis balls (no matter what brand) are made in half a dozen factories in China, Korea, and Japan. Here's the recipe: Soak a flat piece of celluloid in hot alcohol until it's soft, then press it into a hemispherical mold and trim the edges. Once it's hardened, weigh the half-ball, then match it with another of the same weight. Butt them together and cement them with alcohol-based glue. Run each ball through a lot of bounce and flight tests, then grade them. The best ones are ITTF-approved tournament-quality balls; the rest are bought by us slugs who will see how many we can fit in our mouths then lose them behind the couch. Finally, put the balls into a device like a washing machine with small pebbles and sand to smooth their surfaces. Table tennis balls are now 40mm in diameter, up 2mm from a year ago. It's slowed the game, but made it more TV friendly, according to the association.