Ping-pong panelbeating

I have just discovered how to remove dents from table-tennis balls.

We don't have a ping-pong table here, but we do have a lot of ping-pong balls, because we've got four cats and ping-pong balls are great cat toys.

When ping-pong balls are everywhere, though, you'll often tread on one, and dent it. A dented ping-pong ball is of limited utility as a cat toy, and is of course no use at all for actually playing table tennis.

As I was making tea, it occurred to me that just holding a dented ball in tongs and immersing it in very hot water might un-dent it. Even if the heat didn't soften the ball (which, as it turns out, it will), the expansion of the heated gas inside the ball ought to push the dents right out.

And I'll be darned if that is not exactly what happens. The ball swells back up to perfect roundness, and once cooled and dried it seems to bounce pretty much as well as a brand new one.

The only time this trick won't work is if there's an actual hole in the ball, which can happen if a dent has sharp creases. Then, all you get when you immerse the ball is a trail of bubbles from the hole.

(If you subsequently immerse the punctured ball in cold water, the contracting gas inside will suck the water into the ball. This lets you partially fill a ping-pong ball with liquid through a tiny hole, but you could do that with a syringe anyway. I remember seeing a documentary about controlled burning in forestry; to reliably start fires from the air, they used a machine that took ping-pong balls that'd been pre-filled with potassium permanganate, and then syringed glycerine into them, just before dropping them.)

Interestingly, ping-pong balls also smell distinctly of camphor when you take them out of the hot water. That's because they're made of celluloid, which is principally composed of nitrocellulose and camphor. This is why they burn so well:

(Some very, very cheap ping-pong balls are made of plastic instead of celluloid. They're a bit squishy, bounce about as well as a grape, and often aren't even evenly thick all over, so they wobble when rolling. Still OK as cat toys, though.)

Sadly, it would appear that I am not the first person to have thought of this repair technique. But I'm still pleased that I thought it up all by myself.

(I also invented the differential, at about the age of nine. Unfortunately, someone else had already invented that, too.)

11 Responses to “Ping-pong panelbeating”

  1. Donski Says:

    Ping pong balls wrapped in foil and lit with a match make great smoke bombs as well. The lack of oxygen seems to make smoke instead of flames.

  2. evilspoons Says:

    Your blog seems to be denying the fact that I am signed in, again. Argh.

    Anyway, I think sometime in junior high (grade 7-9) I figured out the concept of limits (to a small degree). I was pleasantly surprised the half-baked idea in my head was actually part of real mathematics and the people I tried to explain it to were all just too dull to get what I was talking about, versus me being crazy.

  3. Chazzozz Says:

    Way back in my days with the NSW RFS I actually got to see one of those machines used to fire-bomb forests from a helicopter. Very fascinating piece of gear. What intrigued me the most is that of all the various types of vessels/capsules/whatever they could use for delivery, they actually used real ping pong balls. Perhaps the above-mentioned volatility makes them well-suited for it.

  4. rndmnmbr Says:


    Being the Good Ammurican I am, I own several guns and a reloading press.

    Ping pong balls are made of camphored nitrocellulose, ie. guncotton.

    I wonder if I can talk the rangemaster at the local shooting range into letting me test the effectiveness of ping-pong balls as a propellant. With a bench rest and a wall of sandbags, of course, and a gun I wouldn't mind losing too much.

    I must do Science to it!

  5. Muzz Says:

    I used to do this when I was a kid. I even used to dent them on purpose just so I could do it. It might even have been in one of the Curiosity Show books I had.

    I can't lay claim to getting anywhere with diffs on my own though. It also took me far too long to work out that the egg-milk bottle trick only works if you take the shell off first.

  6. dwalter5 Says:

    I came up with 'Powers of Ten' on my own. For years I thought it would make a great Calvin (and Hobbes) gigantism/shrinkage voyage. Then one day I wiki'd Eames Chair. Glad to know now that I'm not the only one to miss my shot at (already claimed) fame and immortality.

  7. dr_w00t Says:

    I came up with my own Oscillating Universe theory in high school. Was devastated to learn that Einstein beat me to it. Bastard!

  8. Gomisan Says:

    I was going to post about the smoke bomb trick, but someone beat me to it. But to elaborate, make a little handle from the foil to hold/throw it with, and you're just heating it with a flame. As it starts to smoke, ditch it.

    (oh and I wouldn't be breathing it in, it's pretty nasty)

  9. paul_kingtiger Says:

    I remember being so proud when I ran up to my mum and announced I'd invented Safety deposit boxes!

    I also did some work in school with pendulums, the teacher said we could use our own measurements, by which he meant cm or inches. I measured everything based on the length of the pendulum long before I'd heard of algebra or things like pi. This flash of inspiration was dulled somewhat when I decided to call me new unit of measurement a "cooler meter"

  10. stewpot2 Says:

    It must be a mark of true geekdom, to come up with the big ideas independently.

    Back when the Amiga 500 roamed the earth, I pondered long and hard whether it was possible to send a voice signal over a serial link by breaking the signal down into it's component frequencies, sending the resulting spectrum over the serial line, then reconstituting it at the other end. Which, of course, isn't a million miles away from VoIP as practiced today.

  11. mayhem Says:


    You got me all excited about having some fun in the rain over the weekend and then I learned that the Home Office has classed Potassium Permanganate as a drug precursor, so you have to fill out half a ream of paper before you can buy it.

    I'm now weighing up whether it is better to appear to the authorities as an anarchist, a terrorist or a drug maker.

    At least ping pong balls are still readily available...

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