Blow holes, also known as blows, air holes, or gas holes are larger smooth wall shaped bubbles which may be spherical or elongated. They are typically caused by entrapment of air or gasses during the filling of the mold. The causes of the air entrapment can be due to an interrupted pour, turbulent filling, pouring down the riser or improper gating and metal flow. Since the air bubbles float upward in molten aluminum, many times blow holes are more prominent in the cope section of the part