Wood ash has been used since ancient times as a fluxing agent for glazes.
When unglazed vessels are fired in a wood-fired kiln while exposed, only the areas of the kiln that have been covered with ash will melt, forming a transparent, pale blue-green glass body. This discovery probably led to the use of wood as a glaze medium. In Japan, wood was used for all porcelain glazes and most stoneware and pottery glazes in the past. For the production of stained glazes, chair ash was used exclusively, while wood ash was used for pottery glazes. Recently, lime has been widely used in place of wood ash, but wood ash is still used in many cases. The purpose of using wood ash in glazes is to utilize its lime carbonate content.
