Because paint pots are basically made out of mud or clay and then you paint them once they harden.
There are exactly 800000 mud pots in the world i did research on them in egypt a few months back. Hope this helps :)
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Mud/ Sumer
mud pots are form from the weathering of the country rock by hot highly acidic water. The rock is altered often to clay minerals that block the plumbing of the system causing a mud pot composed of alteration products to form.
Mud
This soil is preferred to make pots and toys as it is not like mud and it is easy to dig and easy to work with.
Mud stains can be removed from dry cloth. With the wet cloth wipe it fully. And using soap solution with water remove the mud from auto paint.
If your into the adobe look.may save your paint if you live in the desert.
they made clay pots mostly
You can generally use a clay (mud) pot in the microwave- you should check the bottom to see if it has "microwave safe" written on it.
They mixed berries and mud and paint
it needs to be primed before texture to keep the texture from flashing. If this is not done the paint will absorb differently from the drywall that has no texture or mud on it than the area's that do have mud.