Has anyone come across such a strange phenomenon?

The two photographs show the same Moroccan pot, first during summer, then in winter (the second picture was taken today).

When, initially, in autumn 2020, we saw it turn green, we thought My goodness, it is going to need a lot of brushing off to return it to looking clean(ish) ... but the odd thing was that, without the slightest intervention from us, it turned itself around to a virtually pristine condition. This has now happened three times in three consecutive winter/spring transitions ... as if what we thought was permanently clinging moss would just fall off by itself ...

We find this very strange. Do you? Might anyone have an explanation?

 

Its probably algae rather than moss, would be my guess.
Once the outer surface dries out in summer it cant survive.
Moss shrinks down when dry but its usually still visible.

 

Is it glazed on the inside? as a wine amphora

 

Nice Urn.

 

No, I don't think it's glazed, so damp would be coming from inside, but then so would it in summer, as it is watered daily, but then it daily dries in the midday sun.

Thank you. We love it.
Just tried to retrace its source, but no longer seems to be available.

 

Anything liquid went into amphorae including water, wine, vinegar, olive oil and garum (Roman fermented fish sauce).

 

What's a Roman urn? About 11 euros an hour (apparently).

 

You've forgotten the forty thieves.