All,
I've made a couple of attempts doing some silver casting, and I would appreciate some advice in debugging my process.
I am using a Kerr Electro-melt to melt silver. I am using molds carved from Tufa (a compressed volcanic ash) for which I hope the silver to flow into.
Attempt #1: Flat relief cutting of the tufa. I melted the silver and poured it onto the flat. The silver immediately cooled into balls and did not take an impressions.
Attempt #2: Read that the mold needed to be of a temperature similar to the metal. So what I did was to try to do the casting INSIDE the Electro-melt crucible. I lathed a pair of tufa cylinders, 1 inch long and 1 1/2 inches long. I carved a funnel into the 1 inch long cylinder. I split the 1 1/2 inch long cylinder lengthwise. On one side I carved a pattern complete with sprue holes and air holes. The other side just simply had notches reamed for the sprue entrance and silver exit.
I aligned the cylinders inside the crucible, placed clean scrap silver and a pinch of borax on top of funnel, and ran the Electromelt at 1950 degrees at 10 minutes before cooling it down. I observed that the silver had fallen into the funnel as I had hoped.
After cool-down I found that the silver had completely split the cylinder and that while the flux had entered the pattern, the silver simply wasn't in the pattern. All of the silver that had gone through the funnel had puddled at the bottom of the split cylinder. Further, all the tufa had turned into a glassy kind of stone.
Synopsis: Attempt #2 demonstrated that while simple gravity would cause fluxed silver to move through the funnel, there are other factors requiring correction.
1) Simple compression of the split cylinder inside the tufa was not tight enough, because as the silver expanded the halves of the mold were forced apart. Wrap the halves with iron wire next time?2) Tufa will vitrify. Maybe fire the mold halves and the cylinder first inside the crucible, let cool, and then melt the silver with pre-fired tufa?
My wife tells me: "Back to the drawing board." I think it is a simple matter of debugging, but I wanted to pick the brains of the community for ideas. Also, I don't have much money, so right now I am trying to bootstrap a process with what I have.
Suggestions?
Thanks in advance.
The Eternal Squire