Explanation: blow holes, air inclusions and pin hole porosity are known as “gas defects” in casting. blow holes and open blows are spherical, flattened or elongated cavities present inside the casting or on the surface of the casting. these are caused b moisture left in the mold and core. air inclusions are due to absorption of gases by the molten metal in the furnace, they cannot escape and weaken the mold during casting. these are due to high pouring temperatures. pinhole defects are a form of gas porosity. they are usually small, elongated holes at or immediately below the casting surface with the long axis of the pinhole perpendicular to the casting surface.