Masonry oven India, tandoors are traditional clay ovens, although these days modern electrically fired tandoors are available. The open-topped tandoor is a transitional design between the earth oven and the Roman-plan masonry oven. In the precolumbian Americas, similar ovens were often made of clay or adobe and are now referred to by the Spanish term "horno" (meaning "oven"). Horns are also traditional in the American Southwest. The traditional direct-fired masonry design is often called a "Roman" or "black" oven and dates in Western culture to at least the Roman Republic. It is known as a black oven because the fire generates soot
Masonry oven oven may be wrapped in mineral wool blankets (similar to fiberglass but made from clay or rock and much more resistant to high temperatures and thermal cycling). Mineral wool blankets do need to be covered — either with a reinforced stucco shell, tile, or equivalent. Based on a survey of Canadian clay ovens, Boily and Blanchette suggest an ideal relationship between door and dome height of 63% -- a higher dome will reduce radiant heat, while a high door will allow heat to escape; if the door is less than 63% of dome height, air and smoke can't circulate freely