Bologna bottle facts for kids
A Bologna bottle is a special type of glass bottle. It's also sometimes called a Bologna phial or a philosophical vial. What makes it unique is its amazing strength on the outside, but extreme weakness on the inside. You could even use the outside of the bottle to hammer a nail! But if you scratch the inside, even a little bit, the whole bottle will shatter.
This strange behavior makes Bologna bottles popular in physics demonstrations and magic tricks.
How Bologna Bottles Are Made
Bologna bottles get their special properties during the glass-making process. When they are being made, the outside of the bottle is cooled down very quickly. At the same time, the inside cools down much more slowly.
This fast cooling on the outside makes the glass there incredibly hard and strong. But the slow cooling on the inside creates a lot of hidden stress. This means the inside becomes very fragile. If anything scratches the inside, it releases all that built-up stress, causing the bottle to break apart instantly.
Glassmakers do not anneal (slowly cool) these bottles after they are made. If a Bologna bottle were reheated and then cooled slowly, it would lose its special strength and fragility.
Why Are They Used?
Bologna bottles seem to be a puzzle: they are super strong on the outside but super weak on the inside. Because of this surprising nature, they are often used as props in magic shows. A magician might make the bottle shatter just by shaking a small object inside it, which looks like real magic!
History of the Bologna Bottle
The Bologna bottle gets its name from Bologna, Italy, where it was first discovered. People started talking about these bottles around the 1740s in publications from the Royal Society.
Back then, a glassblower would create a Bologna bottle by letting it cool in the open air instead of putting it back into a special furnace to cool slowly (which is called annealing). This method created the amazing effect. People found that these bottles could survive being dropped from a height onto a hard brick floor without breaking. But if a tiny piece of flint (a sharp stone) was put inside, the bottle would immediately burst!
Even though these bottles can handle strong pushes from the outside, the hidden weaknesses inside mean they aren't used for everyday things.
See also
In Spanish: Botella de Bolonia para niños
