The plaster coat! Actually ours is stucco, the same breathable yellow stuff coating part of the house.
The dome's rosy glow is from a dusting of terra cotta dust I saved from cutting our sconces and outdoor pavements from the old roof tiles [pictures].
Have I said I am trying to use EVERYTHING on the property? The sill under the oven door is broken bits of hand made brick, the walls of leftover porotone (extruded terracotta brick) will be faced with broken brick and stone left over from construction and demolition of the old shack.
Did I say that the fuel will be grape vine and olive and fruit wood from all the clean up of the property? Did I say how much the sugars in these woods flavor the cooking? Stay tuned for the first "fire up."