Link: https://www.youtube.com/watch?v=ca20JkKFAcE

Video notes

Clay is just dirt. Clay can be found in the cracked soil texture or on tire tread tracks.

If the harvested clay is gritty (full of rocks and other impurities) it can be filtered through a regular strainer screen after adding water. After settling for an hour, decant and move into cloth and let dry.

Good clay can be dry processed by just gently pound into powder.

Levigation is continuous decanting after adding water until left with good clay.
The resulting good clay can then be left to dry in a trough, for example.

All clay shrinks when it dries, so it needs temper added, which is non plastic material practically: crushed up pottery (clay after firing), volcanic ash or just sand, most common. A good mix is around 20% temper.