Cut the bronze sprue off the first cast myself and it came away clean
First pour out of a new shell mix went wrong in March. Cold shut on one shoulder, whole piece scrapped. Rebuilt the pattern, remade the shell, and today the sprue cut off with a hacksaw and a chisel and the casting underneath was sound. No porosity, no chasing to hide anything.
Thirty years and I still hold my breath on that cut. You never really know what's under there until you're through.
Foundry man said it was the sand. He's probably right.
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That moment when the saw goes through and you still don't know, and then it's sound. I know that feeling from the other side of things, taking a grout line off a finished panel and hoping the setting bed behaved. Nothing to do but look.
The part I like is no chasing to hide anything. That is the real win, not the casting itself. It means the March failure got fixed at the source and not covered up. Mold man blaming the sand is convenient but he isn't wrong either, the shell is half the fight.
Grout line off a finished panel. That's worse than my cut, at least with bronze I can weld it back. Nothing hides in a grout line, it just shows up.
And yes, fixing at the source. A guy who chases porosity with a torch is just delaying the phone call from the client. The shell was the problem, the shell got remade. Sand man can take his bow, he earned it.