Could a material exist that is glass-like on the outside but spongy on the inside?

In my DND world, I've established that there is a substance that has these properties:

1. It is made from a chalky "dust" that can be mined
2. The dust gets mixed with unspecified chemicals to create a clay-like, slightly sticky substance
3. The clay-stuff gets cured in another unspecified chemical mixture, at which point the outside gets hard and brittle like glass (and shatters like glass)
4. I haven't actually said this to the players, but my thought was that the curing process only cures the outside, and the inside stays spongy

This substance can be used for lots of minor magical feats, so of course my players want to experiment with it, to see if they can get it into weapons.

When I designed this, I wanted a substance that could not easily be made into a viable weapon, since true magic weapons are extremely valuable in DND, but can be sculpted by artisans before being cured. That's where I got the idea of the outside becoming glass-like. The part with the inside being spongy is optional, if it just doesn't make sense. The idea there was for it to gradually get dried out on the inside as it's used, so that it only works for a period of time, creating constant demand for the stuff.

When I had a player ask about making weapons with the "dust", my initial thought was that it would be like mixing glass with metal, but that apparently can't be done. (Can You Mix Glass in a Metal Alloy?)

So, now I'm wondering if I can let them discover a scientifically sound way to get this stuff into weapons, keeping the short-term feeling of the original substance. But having the process be scientifically sound requires that the physical characteristics of the substance are able to exist in the first place.

Does (or could) a substance like this exist, and if so, what are its physical/chemical properties, especially pertaining to making metallic alloys out of it?

posted over 4 years ago

Kristen Hammack‭

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