The clay-slurry sits in the sun so that evaporation may run its course. In these basins (compare to the image here) the clay is now ready. It will be scraped up and hauled inside. It will be kept cool and moist until the time comes for the potter to turn it into ceramic vessels.
These basins are part of a ceramic production center found in al-Khalil (Hebron), Palestine.
Note the litter of potsherds at the bottom of the image.