Originally Posted by
loader
Well I went to home depot and got sawdust from the vertical saw for cutting plywood. Guess I need to toss it, according to you. I can't assume that you have a dedicated, safe casting setup with sufficient ventilation to keep you from huffing bad fumes, hence the caution. Like Rick said, plywood sawdust is fine as long as you don't breathe it. Pressure-treated lumber, while not at bad as it used to be before the EPA banned the arsenic content, it does contain significant amounts of copper compounds and other stuff you shouldn't ever breathe.
Thanks for the write up, gear, but I didn't have chemistry in HS. Lost cause. I can gather that Carbon gathers inpurity, and blends tin in the alloy. I used Borax to flux, and did not remove anything, that I could see anyway, form the pot. Uhh, not exactly. You can't see tin in suspension without an electron microscope. The carbon is reacted chemically and changed into carbon dioxide gas. The other part of the chemical reaction (redox) is that the lead, tin, and antimony oxidesgive up the oxide part and they are transformed back into pure metals. The ash that remains together with some unburned carbon actually does act like a physical sponge, soaking up impurities. Sort of. It's more complex than that, but that's the gist.
So by using the borax with WW's what happened to the tin? It's in suspension? And will not do it's job... help lead to fill out the mold? The tin and other metals are in suspension with the borax, not the liquid metal. The borax sucks them up and holds them forever. You throw away the tin with the dross, no way around it. A small amount of tin helps fillout by creating an oxide barrier to the molten lead as it flows, like a shield. The tin flash-oxidizes on the surface of the lead, and since tin oxide is more flexible than lead oxide, it actually makes the lead flow better by keeping the lead surface from oxidizing as it flows into the mould. Basically, tin makes lead flow like water instead of pancake syrup.
What can I do to fix the ingots I made with fluxing with the Borax? Will the sawdust bring tin out of suspension? No, once the tin gets sucked up by the borax, it's gone. Probably not anywhere near all of your tin was trapped by the borax, so don't worry too much about it, but some was lost to be sure. Just add a half-percent back and you should be fine.