When u have voids in the casting with sharp edges like that u have plaster breaking out and flowing with the gold. When u quench it goes away and leaves the voids. Prob a spruing issue or very thin areas of the model or sharp corners or is using a centrifugal casting machine too many turns on the spring. Lots of things can cause plaster breakout. Make sure all sprue contact points have rounded contact points. No corners or sharp flow points.
Don't know how small the clean out holes are in the diamond seats, but if u spin or pour metal this is a great place for plaster breakout. I only drill or model "pilot" holes for smaller diamonds and stones. What investment are u using?
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