New Ingot Mold

[lazersteve]

Hello Everyone,

Today I got a new cast iron ingot mold. After four attempts at making a decent bar I poured this one:

I had to use a scrap piece of graphite to get it to fill the mold that's why it's slightly irregular. I'm going to fashion a properly sized piece of graphite to press the molten gold so future ingots will turn out more uniform.

The ingot weighs in at 27.5 grams.

Steve

Steve

 

[Harold_V]

Nice job, Steve.

I think you'll come to discover that in order to fill a mold, the volume will dictate cavity size. While pressing may work, it's likely to be a real challenge to end up with an ingot that isn't strange in appearance, and you have precious little time to react once the gold has been poured.

How I regret not having some pics of the various sizes of ingots I used to cast. Not to show them off, but to provide some guidelines on sizes that will cast successfully. Once you get below an ounce, they become quite small. They'll pour beautifully if the mold is the correct size, leaving you with a full loaf, and no projections. Casting a thin ingot borders on the impossible unless you use a closed mold (end pouring, with a sprue, as GSP discussed recently for silver).

Harold

 

[goldsilverpro]

If you want ingots that are flat on all sides, you need a graphite book mold. This is a two part mold. One part has the cavity and attached to the cavity is a groove continuing to one edge. The other part is just a flat graphite plate. The two parts are clamped together and set on edge so the groove is facing upward. The gold is poured into the groove and fills the cavity and at least part of the groove. When the gold is removed, attached to the bar is the gold that filled the groove. It is sawn off, flush with the end, leaving a bar with 6 flat surfaces. The groove is called the sprue, I believe.

I used book molds for many hundreds of 10 and 100 oz silver bars that I produced.

To me, the most beautiful gold bars are open faced with crystals and sinks. Of course, they won't look so great if they're not pure. I wouldn't buy a supposed pure gold bar unless it were open face and I saw crystal and a sink.

 

[Harold_V]

To me, the most beautiful gold bars are open faced with crystals and sinks. Of course, they won't look so great if they're not pure. I wouldn't buy a supposed pure gold bar unless it were open face and I saw crystal and a sink.

Yep! I agree. Hoke talks about the characteristic "pipe" that forms when pure gold cools. I've seen cavities pulled in buttons that were over 1/8" deep, and no larger in diameter. The button displays a wonderful coarse geometric pattern, and is shiny where there are no lines. All of that goes away with very little contamination.

When casting ingots, you can eliminate the pipe by waving a torch over the surface as the ingot cools, keeping the entire surface molten instead of allowing the gold to chill from the outer edge towards the center. That practice, well executed, will yield a surface that is very good, and almost flat. If there's contamination in the gold and an oxidizing flame is used, the gold will display oxidation. That's an excellent way to help determine if gold is pure, or not. The slightest thing changes how gold cools, or its color, and the contamination need not be base metal.

I had occasion to re-refine some gold that had been marked 9995 pure. There's no way it was---obvious by the surface finish and color. When it was re-refined, platinum was the contaminant. It may be worth money, but it costs money to eliminate, so it's not welcome in gold any more than copper or silver.

Harold

 

[lazersteve]

Chris,

That's how this bar looks on the edges where the graphite press didn't contact the gold, like fine crystals around the curved surface of the ingot.

I'll try adding the proper weight of gold to the mold to get the ingot to form properly tonight.

The photos of the nugget I posted previously show the crystal lattice and piping you and Harold speak about:

You can clearly see the crystal lattice and dimpled pipe in the center.

Steve