secondary part for overheating gold. Any idea what happened?

[duhiliketolick]

A friend brought a home foundry with the correct crucible. Using borax (Muleteam)on crucible, took some powder (was processed Ap- HC CL-SMB- siphoned- air dried) put in. Observing through vent hole watched powder liquify into molten substance. Crucible was too deep to fully see any color. Poured out let cool. It is black on surface but if you scratch it has a silver appearance. :?


Once again Steve comes to our rescue. Thanks again.
Very Happy

 

[bmgold]

I'm waiting to see an answer to your problem. I just did another small test out of impatience. I took some precipitated powder that was not washed and tried to melt it. I got a brown stained flux with some red color. There is a line of ?gold? beads (very tiny) in the flux. This never melted together into one bead.

There was a couple other larger beads that were a silver color with a dark coating. I was able to smash this little bead of metal with plyers so it is soft. My guess is either lead or tin from solder but I don't really know.

I suspect my problem is contaminating metals from the unwashed powder. I wonder if I either had too much flux or just not enough heat or time to melt the little beads into one lump. Also, the tiny quantity of possible gold makes it hard for the tiny particles to join and makes it easy to lose the gold in the dark flux.

Somebody else will probably jump in with the answer to these problems but I would guess that your powder was not washed or not washed enough to get rid of the contaminating base metals. Don't throw anything away! I'm sure there is a way to recover your gold. It is still there (somewhere).

 

[lazersteve]

This is not uncommon with dirty gold as you both have come to realize.

The short answer is that your gold is not very pure.

It is likely contaminated with silver and copper chlorides. At furnace temperatures these chlorides will decompose into the respective metal and metal oxides. These oxides and metals alloy with the gold and produce the crust upon cooling.

The problem is due to any one or all of the following.

1. Your solution was not properly filtered. The solutions must be 100% transparent with no particulate or cloudiness. Remember that diluting the acid auric chloride will cause nearly all silver chloride in solution to precipitate. This small amount of silver chloride has to be removed from the solution or it will end up in your gold powder.

2. You did not remove all of the base metals from the gold before it was dissolved. Your solutions should be yellow to deep orange red.

Any sign of blue or green is a strong indication of copper and or nickle contamination. Copper in the solution will precipitate as copper I chloride when an excess of SMB is used or if copper levels are very high.

3. You did not properly wash the precipitated gold powder. Here is a link to the washing technique:

Filterless wash process

This method is a slight variation of Harold's method and he deserves the credit for the process.

4. Your dish or torch induced the contamination. Always use a good clean dish to melt your metals. Always dedicate a dish to each type of metal (Gold, silver, etc.). Clean your dishes with molten soda ash.

To fix your nugget you will need to redissolve in AR and strictly follow the processes above.

Steve