Traditionally, carpenters burnt the wood on site. In the procedure, three boards of Japanese cedar sugi are bound together with a wet rope to form a triangle pillar shape. After binding the boards tightly, fire is ignited on the bottom with some rounded paper or newspapers. In the past, sawdust was used instead of newspaper.
When the triangular pillar is put up, it takes a minute or two for the fire to proliferate and starts to quickly spread due to the chimney or stack effect from the triangle of boards. When the surface of the plank is sufficiently burnt, the triangular pillar is open and the fire is extinguished by applying water to cool it. The combustion time is about five minutes.
Since the 1970s, innovation in machines allowed cedar wood to be charred with high-temperature burners at 1700 Celcius on all four sides. Originally the process was done by hand but today the mechanization process is now generalized.