In the photo am I seeing little round voids made of investment inside the material itself?
So if that's the case, two things.
One- Contaminated wax. Keep your wax, your sprues, and even your waxing tips, very clean.
Two- Die lube... folks like to smother their dies in lube several times between dipping and finally sealing the margins. If there is a lot of lube it becomes voids in the shoulder. And since its just good science, they're perfectly round voids made up of bubbles of lube. Then when you invest, this investmen fills these little pockets where lube was. Keep your waxups adapted very well on the intaglio surface and blot all your lube with a tissue before dipping and/or sealing.
I'm thinking its two...
Usually contaminates are black/burnt, and most often get pressed into the margin.
So just start keeping everything, VERY REDICULOUSLY CLEAN, and ease up on the lube to avoid voids made of lube.
"Avoid voids."-Interesting
Anyway, I have tins of grey thowax that say, "KEEP CLEAN!" But people still leave them open and even grind on things at the same bench. So I have to scrap it and buy another. Gota gota gota keep it clean...
Besides the photos someone on this thread was having issues with bubbles while layering ceram.
It's not necessary, but since they are having issues, I would suggest using Acid to remove the reaction layer as well as a good sand blasting...
Ivoclaire sells "Emax Invex Liquid." A diluted hydrofluoric acid you can use to ultrasonic that layer off.
Even if it looks like you've blasted it all off, its sometimes still there. And you can see it when you acid wash it and you'll say, "hey marc was right, look at that, it IS still there."
