The development of Korean glaze originated from the development of ash glazes. Ash not only has strong solubility but also can shows the glaze a variety of different colors according to what the glaze has in it as the main component. In addition, it gives a feeling of lucidness and softness. For these reasons, there are a lot of needs for ash and many potters want to take advantage of ashes as glaze. But natural ashes have not been widely used as glaze primarily because it is relatively hard to find or manufacture. Considering the difficulty of finding or manufacturing natural ashes, this study aims to formulate synthetic ash which not only is available to the potters in general but also has the sam ε characteristics as the natural ashes. To achieve this aim, this study examines the characteristics of the pine tree ash, the main component of the glaze of celadon porcelains, and the red pepper stem ash, the main component of the brown glaze, both of which have been used by the Korean traditional potters. In this study, the alkaline component of the glaze. A important ingredient when the ashes are synthesized, was supplied by mixing of $Na_2CO_3$, Chungju limestone and rice straw ash. Furthermore, the synthetic ash, when it shows no change of pH in its composition rate of 6:2:2, was found to be usable as the most stable material. In conclusion, the formula which frits some raw $materials-Na_2CO_3$, Chungju limestone and rice straw ash-can duplicate the synthetic ash which is simila to the natural ash.