Clay is dug up everywhere in the world. Dug up is just the beginning. Then any organic materials are removed (leaves, roots, etc) by using a series of sieves. Any microscopic organics will be burned out of the clay in the bisque firing.
The clay is then broken up and dried. After it is dried, it is broken up even further and water is added then let to rest or “slack” until the clay has absorbed the water. It is mixed and other ingredients are added (kaoline, colorants, talc, etc).
Keep in mind that there are places where all this is done by hand- no machines!
Pugmills and clay mixers are the machines that we use to help in this total process. There are some that are both a mixer and pugmill or you could use two machines.
The clay is mixed until it is the correct consistency to throw. So now for pugging. As the machine pugs it will remove the air from the clay and extrude it out for you to bag up.
Do large scale sellers go through all this work? Probably not. They buy the ingredients from companies that mine each ingredient. They have developed clay bodies by the R&D department doing constant testing.
What if you have a small studio & can’t afford a mixer or pugmill? Set up an area for recycling. Use large containers & put all your scraps in it as you go. When it is full, add water until the clay scraps have dissolved and are a sludge consistency.
Use pottery plaster to make plaster slabs to dry the sludgy clay until it is the correct consistency to throw. You will have to flip over your clay when ½ way dry. Then divide the clay into pieces the size you want to throw. Now wedge until the air has been removed. While wedging cut the clay in half. If you can see the air pockets, keep wedging.
So buying this bag of clay supports your local clay store, the company they buy the clay from and the mining industry. Lots of people for the small price of a bag of clay.