Abstract: A gas permeable ceramic investment mold is disposed in a casting chamber and filled with melt to be solidified via a mold melt inlet, such as for example a mold pour cup adapted to receive the melt from a melting crucible in the casting chamber. After the melt is cast into the hot investment mold in the vacuum casting chamber, a pressure cap is positioned in sealing engagement with the mold melt inlet, and gas pressure is introduced through the pressure cap to provide selective or local gas pressure on the melt in the mold without pressure cracking or other damage to the relatively fragile investment mold, while the casting chamber is maintained under relative vacuum or a different pressure from that in the mold.