The artisan make different decoration blocks out of clay. He would trade in iron or meager amounts of emerald for different types of pots, cutlery, and sculptures. These would be cheap as clay could literally be found on the ground, in riverbeds and riverbanks.
The artisan would provide a great way to add more intricate decorations into Minecraft, opening many door in buildig. Perhaps different decorations could be dyed in different ways, too. There can even be more types of materials, such as ceramic, silver, marble, or the already in-game glass, iron, gold, quartz and wood.