The inner surface of the defects was basically composed of oxide and lustrous carbon films, and sometimes additional oxide films were observed on the dual films. The lustrous carbon films exhibited clear folds or creases, and some of them were broken through or were deformed by dendrite growth. The formation mechanism of the dual layer and its characteristic features could not be explained by authorized theories. But it can be explained by assuming that the films on these defects are generated on the surface of the melt and are entrained in turbulent flow. In addition, many small pores in size of 100 - 200 μm were detected around porosity defects, of which inner surface were composed of lustrous carbon films exhibiting clear folds or creases.