potter's clay vs potter's earth

potter's clay and potter's earth both are nouns.

Word	Noun	Adjective	Verb	Adverb
potter's clay	Yes	No	No	No
potter's earth	Yes	No	No	No

As nouns, potter's clay and potter's earth are synonyms defined as:

potter's clay and potter's earth: clay that does not contain any iron; used in making pottery or for modeling

potter's clay (noun)	potter's earth (noun)
clay that does not contain any iron; used in making pottery or for modeling	clay that does not contain any iron; used in making pottery or for modeling