Investigation of the tasteful "Sabi" phenomenon of the aged Kyoto wall

Kyo-wall is the earthen wall composed of clay containing sand and plant fiber, which is manually kneaded and plastered with the trowels to form there layers inducing the natural and aesthetic surface appearance. Kyo-wall is the traditional technology produced for the compact room to hold Japanese tea ceremony created by Sen-no Rikyu in 16th century and have been succeeded to Kyo-machiya house up to now. The top surface is smoothly covered with clay causing minute aesthetic appearance and the color which is ocher initially becomes to have the dark spots called "Sabi" gradually a few months or a few years later. Sabi has been appreciated as tasteful rust phenomenon of the aged Kyoto wall. However the mechanism of Sabi phenomenon and their control factors have not been understood and have been believed as iron rust caused by air oxidation until now. In this study we have applied the low incident angle X-ray fluorescent mapping technique to get the mineral elements distributions of the top surface of Kyo-wall with Sabi dark spots and Si, Al, Fe, K, Ca, S, Ti, Mn are detected as more than 0.1wt% content. And we have found that only Mn density pattern fits the Sabi spots distribution and Fe density have no connection with the Sabi spots distribution, It is kown that Sabi occurs not on the shaded surface from the wind but on the open surface in the wind and can be seen also in the process of roof tile Kyo-kawara or porcelain Kutaniyaki surface containing clay. Mn ion in the interface water layer of the clay structure seems to bleed out to the surface due to asymmetric turbulent wind flow and to be oxidized by the air. This newly found secret hidden in the traditional technology will be applied as the future technology.