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Rio suggest covering cooling button with a charcoal block?

I’ve seen a lot of discussion on here about charcoal blocks for soldering.

In this how-to video for their vacuum casting machine, they suggest placing a charcoal block over the cooling button after removing the flask from the vacuum.

Does anyone have any experience doing this? Does it work, and help, to reduce oxides from forming?

And is there a reason to wait until after the vacuum is turned off (60-90 seconds after pouring), and not put the charcoal on immediately after the pour?

It doesn’t seem like the charcoal just sitting on top and smouldering would be able to “pull” that much oxygen out… can anyone explain the principle here?

In my mind this seems more like a way to keep the surface clean.
The interaction between the heat and the charcoal will create a oxygen deprived atmosphere which
may benefit for the most part Silver and other alloys which react to Oxygen.
I have seen it done on smelting/melting Silver alloys in gas furnaces,
but then the charcoal/lumber piece sits on top of the molten metal at all times.
So maybe there is more to it than I think?

I’m considering doing it when casting bronze. I was using Rio’s Ancient Bronze casting grain, and I got loads of firescale the first time. I now have a charcoal block, and I’m considering putting on the hot button to see if it helps.

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