According to mishna Keilim 4:4, earthenware is not susceptible to tumah until it has been baked in an oven.
כלי חרס מאימתיי מקבלין טומאה? משייצרפו בכבשן, והיא גמר מלאכתן.
When does earthenware become susceptible to tumah? From when one bakes it in an oven, and this is the end of their manufacture. (translation partly from Kehati)
Nowadays, one can purchase air-dried (or self-hardening) clay, which is clay with some additive to make it harden even without firing.
Are pots made from air-dried clay susceptible to tumah? Do they have the status of earthenware vessels (כלי חרס), and so are not susceptible as long as they aren't baked? Or perhaps since the completion of their manufacture does not involve an oven, they are susceptible to tumah as soon as they're ready to be used?