Deebrief wrote:
What is the best paint to use, in order that it does not flake off.

I'd say exterior emulsion intended for painting walls. But you can't
ordinarily get that in a full range of colours, or in small tins. On
the whole, I'd say that any ordinary paint, including artists'
acrylic, would do if you seal the whole thing inside and out
afterwards to make it harder for water to get under the paint film.
The best sealer would probably be the two-pack gel-coat you use to
finish off a GRP boat. This would also help to protect the pot
against frost.

(You can partly frost-protect pots with a masonry water-proofer; but
I don't think these will take well over paint.)

Mike.