The study was intended to investigate production tools and conditions of oil spot following calculating optimal composition of oil spot tenmoku glaze which can be produced at 1250$sim$l260$^{circ}C$. Since oil spot is influenced by the viscosity of glaze, viscosity of various glazes fit for oil spot production was determined by an SciGlass 6.0-based calculating method. Applied amount and calcinating conditions of the resulting substance of oil spot, $Fe_2O_3$, were analyzed. As a result, the viscosity of the glaze durable at 1260$^{circ}C$ was found to range from 4.2 to 4.4, natural cooling was used after oxidizing calcinations at 1260$^{circ}C$ for an hour, and the best oil spot tenmoku was produced by the natural cooling process after 1 h calcinations at 1150$^{circ}C$ in the middle of natural cooling. Also, the study showed that thickness of glaze was found to have an effect on the production of oil spot and resulting oil spot was filled mostly with $Fe_2O_3$.