Pitting is a common problem in investment casting that can be avoided through proper procedures. Contamination from extraneous substances can result in pits. Poorly designed sprues cantrap air, which may form bubbles. Overheated alloys can create gas bubbles, which leave voids. Under-heated molds can leave residual wax, that which can also cause pitting. There are other causes as well. Make sure your foundry has an effective quality program to avoid these issues.