Crucible questions

[bswartzwelder]

After I treated my small placer nuggets to poorman's AR, not all of them dissolved. After filtering, I found a lot of small pieces of what looked to be black nuggets, although they were much smaller than the original nuggets. I placed them in a crucible added some flux, and put the crucible into my home made forge. After a while, everything had melted, so I poured it into a cast iron conical mold. As I was pouring it, the consistency of the pour was similar to honey. I have read somewhere that by adding more flux, you can make it thinner and easier to pour, although I haven't tried this yet. After cooling, I chipped/broke away the black obsidian like glass and found a piece of what appears to be gold. It weighs in at 11.4 grams, but there are still a couple of small pieces of the glass attached.

I assume the black glass from the mold may still hold some values. Don't know if they would be worth recovering, but, I would think the best way would be to crush everything into a powder and treat with either poormans AR or acid/Chlorox to re-dissolve any values. I have about 10 of these little black cones, so I would like to process them all at one time.

Also, there is a thin film of the black glass on the side and bottom of my crucible. It appears to have some shiny powder in it. The powder looks to be the size of flour (very fine). The black coating on the crucible sides is cracked, probably from thermal shock or cooling down, so I would think it could be picked off. Does anyone worry about this flux on the side of the crucible, or do you just assume it will be replaced with "new" material the next time the crucible is used? Eventually, when the crucible wears out, I would think you just break it up to release the flux on the side/bottom.

Am I on the right track?

 

[JHS]

try this
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=582

 

[Harold_V]

I have read somewhere that by adding more flux, you can make it thinner and easier to pour, although I haven't tried this yet.

While you'll enjoy some success by adding more flux, the smart thing to do in a situation like this is to add some soda ash. The hard coating you described sounds a great deal like it could contain silver chloride, which would be reduced to elemental silver by the addition of soda ash. If, after using some soda ash, you find your flux still too thick, consider using a small amount of fluorspar. It will render your flux water thin, resulting in a better recovery of values, in particular if you find prills in your flux. Be advised, fluorspar as well as soda ash are hard on refractory materials.

I assume the black glass from the mold may still hold some values. Don't know if they would be worth recovering, but, I would think the best way would be to crush everything into a powder and treat with either poormans AR or acid/Chlorox to re-dissolve any values. I have about 10 of these little black cones, so I would like to process them all at one time.

You may enjoy success by simply adding soda ash and fluorspar, and remelting. Unless you find prills in the flag right now, crushing and panning isn't likely to bear fruit.

Also, there is a thin film of the black glass on the side and bottom of my crucible. It appears to have some shiny powder in it. The powder looks to be the size of flour (very fine). The black coating on the crucible sides is cracked, probably from thermal shock or cooling down, so I would think it could be picked off. Does anyone worry about this flux on the side of the crucible, or do you just assume it will be replaced with "new" material the next time the crucible is used? Eventually, when the crucible wears out, I would think you just break it up to release the flux on the side/bottom.

Did you make mention of the type of crucible you're using? If so, I missed it.
Unless you've experiencing boil-over, the material you see on the exterior is most likely nothing more than the glaze that is applied to crucibles to prolong their useful life. If you use a good flux recipe and "cook" the charge long enough for things to agglomerate and settle well before you pour, I expect that your crucible won't have much value when it's time to dicard the thing. Check it for obvious signs of values being left behind, then, if you find nothing, toss it. Remember, a crucible is intended to withstand everything we must do in the process of melting and smelting--so it will be correspondingly difficult to process when it's time to discard the thing.

If you use a good flux recipe and cook long enough, assuming there's something in the charge that will behave as a collector, you can achieve a level of recovery that is so good that it isn't economical to re-process the resulting slag with litharge. Been there, done that. 8)

Harold