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
Ceramic foam of the earliest and still most common is the polymeric sponge method. A polymeric sponge is covered with a ceramic in suspension, and after rolling to ensure all pores have been filled, the ceramic-coated sponge is dried and pyrolysed to decompose the polymer, leaving only the porous ceramic structure. The foam must then be sintered for final densification. This method is widely used because it is effective with any ceramic able to be suspended; however, large amounts of gaseous byproducts are released and cracking due to differences in thermal expansion coefficients is common. While the above are both based on