Left mound radical
阝 — the contracted form of
阜 (hill), the indexing radical here when
阝 is on the left (Kangxi #170 fù). Pottery was traditionally made by digging clay from hillsides, so the mound is literal — clay-rich earth. Same left-
阝 anchors
院,
防,
阴,
险. (Right-side
阝 is unrelated
邑 'city'.)