I agree with @wild edges - I think it looks more mineral than organic. Is the close-up pic it looks like the pot has (or had) some kind of paint or coating on it - could that be what's deteriorating?
I think I would put the Ficus in a new pot, mostly because I'm not keen on the "distressed" look for indoors, but also just in case it's a nasty, and use that one outside (maybe try giving it a scrub with a stiff brush to see what comes off).
Doncaster, South Yorkshire. Soil type: sandy, well-drained
pretty sure its caused by salt/minerals leaching out of the terracotta, we get it on our old bricks on and lime plaster anywhere where we have damp Will be caused by the pot being damp a lot of the time, won't do any harm and should just brush off with a cloth or brush if you let it dry out
it tends to occur on the opposite side to the moisture, so as the water soaks into the pot from the inside, the water evaporates and the minerals in the pot/or water (do you have a water softener by any chance?) leach out of the other side
it tends to occur on the opposite side to the moisture, so as the water soaks into the pot from the inside, the water evaporates and the minerals in the pot/or water (do you have a water softener by any chance?) leach out of the other side
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The pot has never been painted.
It sits on the floor and we have underfloor heating. I'd have thought that should stop the outside of the pot being too damp.