# Prince Rupert's Ring

Is it possible to make a toughened glass ring with Price Rupert’s Drop-like properties by forming a torus of hot glass then dropping the whole thing into water?

I know the glass for PRDs is normally molten to a liquid state, but I don’t think it would be very hard to contrive a device that extrudes and shapes glass into a ring shape whilst keeping it hot enough.

Would this result in a PRD with no ‘tail’ and therefore extra durability?

As I understand it, tempered glass always ends up with a weak point somewhere. When the shape includes a point, that’s usually where the weak point is. But even if it doesn’t, there will still be a weak spot; it’s just harder to tell where it is.

And I misread the thread title at first as being about a different prince with a ring associated with his name.

If you just want a toughened glass ring, it may be possible:

I’m not sure if a perfectly symmetrical torus would have stability issues or not, or how tough it would be, but there appears to be no barrier to creating one.

I’m not sure if the ‘weak spot somewhere’ is an essential part of the phenomenon (like the stress-balancing version of Hairy Ball Theorem) or if it’s just an accident of the way things are typically, but not compulsorily made.

For example a sphere of molten glass cooled rapidly and evenly across its entire surface area should - I think - result in the whole of the inside volume being under tension, pulling the outside surface inward, rendering the entire surface strong (the ‘weak point’ here being inaccessible inside the sphere).

I’m not sure it’s possible to cool it uniformly enough to do that, though. You can’t just drop it into a bucket of water, for instance, because there’s always going to be some spot that enters the water first and some spot that’s last.

Tempered Glass windows are made all the time without there being any “hairy Tennis Ball” weak points: Tempered glass - Wikipedia

The reason that Prince Rupert’s Drops have that shape is that they’re easy to make that way – you take the glob of molten glass you’re working with and drop it into a bucket of water. The skin immediately cools and you get that characteristic temper over the surface, making it tough and capable of withstanding surprising pounding – except I that vulnerable tail.

In principle it ought to be possible to get a torus to temper evenly all over, but I have no idea how you’d go about manufacturing one as a practical matter.
The OP should’ve included some links – Prince Rupert’s Drops are a fascinating yet not very well-known phenomenon:

High Speed video of the drops: