[benwiggy]

Hello. I did chemistry at school and a bit at university, and even taught it, but haven't really used it for twenty years, and some it seems to have gone.

I have a Moka coffee pot, and the bottom section where the water is boiled seems to grow crystals of .. something after use (and washing). I don't seem to get it on any other parts of the pot, nor on any saucepans or other kitchen stuff.

It's quite a hard water area, so plenty of salts in the water, I'm sure. CaCO₃, ions of Mg²⁺, Cl-, F-, K+, etc. Now I'm presuming the pot is made from Aluminium, but it could be something else.

Is it just crystals by evaporation, or might the process be encouraged by some interaction between the metal and the ions in the water? Something to do with the Activity Series? And is it relevant that it is the heat-bearing surface that is most affected?

[Borek]

Perhaps just a hard water scale.

[benwiggy]

Despite the fact that nothing else in my kitchen seems so affected? OK.

You can purchase little silver things which claim to remove tarnish from metalware, presumably by a similar, but reversed, action to what I was thinking was going on here.

Ok, crystals by evaporation it is.