The purpose of this paper is to clarify the historical transition of the purification cortex techniques called "ARAI" in Japanese traditional architecture. "ARAI" is one of a sophisticated traditional technique, in order to preserve the old wooden Japanese architecture. It is also important in the problem of what to do with the patina when we preserve an ancient architecture. To clarify the history and techniques of "ARAI", the investigation of the historic document and the hearing survey to the workmen are done. Then we verify aesthetics of an ancient wooden building technique considered from the purification cortex.
