I cast buttons in stone molds. Usually air bubbles don't matter because they end up on the back side which isn't seen anyway. For this button I seem to need channels, and I'm not sure how they work. I made holes by the red circles that weren't enough. I could make more along the split between the two top pieces, or anywhere on the surface of the bottom piece, but I'm worried if I go ham too much metal will flow out of the mold and I won't have a complete piece because of that. Any advice would be helpful. I can generally patch up holes I've made, but I'd rather get it right the first time.
I don't think anyone here has ever used stone for a metal mould, there would be risks of the stone shards flying off once the stone got hot from repeated use and the moisture inside got hot enough to convert to steam. What metal are you casting zinc, aluminium, Zamac alloy?. You might be better off making some machined or carved dies in grey cast iron and preheating it before pouring metal.
75% tin 25% lead. It's just a few grams of metal, I very much doubt anything could go that badly with so little energy involved. Casting in stone is what people did for 5000 years before dies were invented.
Did you preheat the mold? Stone has quite a lot of heat capacity and could be causing the metal in the thinner sections to freeze before it's able to completely fill the mold.
I've had that problem before, it looks different. I asked on reddit as well and they suggested tilting the mold slightly, and that worked, so issue resolved.
Linus, Here's a thread that might interest you. It's done by a Swedish archeologist who researched the methods used by bronze age Vikings to do lost wax castings.. There are several papers that explain it in detail. Viking lost wax bronze casting.. | The Home Foundry
