How do glass companies know how to mold an hourglass to have the sand fall precisely?


How do glass companies know how to mold an hourglass to have the sand fall precisely?

In: Technology

They don’t need to. They mold the hourglass to have sand fall approximately, add sand, wait the hour, dump the extra out and seal the glass. Its WAY easier to calibrate the sand than to calibrate the neck.

They don’t. They manufacture one and figure out how much sand it needs for they time they want, once that is settled they can mass produce exact copies of the hourglass and use the same amount of sand in each.

Minor variations will exist of course from minor variations in manufacturing or even the granules of sand.


Wow I was legit just thinking this question in my head on the way to work this morning. Are we all thinking about it due to Aladdin being out in cinemas?

Related question: How are hourglasses made? Is it one piece of glass that is blown? Or two pieces that are joined in the middle/the choke point? When does the sand get added and through what opening (at the end or at the chokepoint)? Does anyone have a video how they are produced?

These answers are probably right in practice, but you absolutely can model the sand as a fluid flow and determine flow rate based upon neck size. Then you can scale very easily to any time or glass size.

I wonder if the more use an hour glass gets, the more out of time it gets.

considering the sand is always getting smaller and finer, the more you shake it up, or mix it, turn it over, the (ever so slightly) more bits of sand rub up against each other and smooth off the edges, making each part smaller.

also, the hole might get bigger too?

The answers are so often a thought experiment about how it could be done, rather than a definitive statement about how it is done.

Bonus question with answer:

Q: How do thermometer manufacturers know how to blow glass so that the alcohol or mercury expands perfectly to tell you the temperature.

A: They don’t. They get it close, then put the thermometer in fluids at a two different known temperatures then mark the glass. Then they pick the correct pre-made stencil to fit those two markings and paint the rest.

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