The factory made their own clay and the Yixing clay is very famous. It is dug locally and has great properties. There is a lot of Mica in the clay body and it allows it to retain heat well, It is also more technical than that but I will leave that knowledge to those who really seek it. Moving on, here is a pile of the local clay and it is left in the sun and weather for many days before being processed. This is the yellow, I think and you can see a bit of iron in it now.