Crystalline growths

A local deli has a glass-enclosed counter where they keep the various ingredients and condiments in plastic containers, so that the customer can point and choose what to fill their sandwiches with. The containers sit in a sort of shallow metal tub, the kind you might fill with heated water to keep food warm.

What I noticed today was that the surface of this tub is lightly sprinkled with a kind of white crystalline material looking very much like frost – clusters of little star- or snowflake-like shapes. I am fairly sure that the counter isn’t refrigerated, so I rather doubt that they’re ice crystals.

I remember having seen something similar before: When I moved into my previous apartment, the bathroom had a ceiling lamp whose cover had a similar, crusty crystalline matter that seemed to be growing on it. It might not be the same thing, though.

What’s this stuff? There’s no living matter that is crystalline, that I know of, but perhaps there’s some kind of fungus that just looks that way.

(Could it be mildew?)

I have no idea what it could be but it occurs to me that one easy way to find out would be to ask the people in the deli :slight_smile:

Likely a residue from a cleaning agent. Sodium tripolyphosphate or ammonium chloride are possibilities, or it might be the salt of a detergent.

Could also be hard water residue, again from the cleaning.