Chondrule
Active member
Hi folks,
I processed 395 grams of miscellaneous silver jewelry from the 60's and 70's (my mom cleaned out her jewelry box) using nitric and copper to do the precipitation. The shot I produced is silver in color like it should be and always is, however it's shiny, kind of mirror-like. The thing is, I then inquarted some gold with this contaminated silver, figuring the contaminant would remain in solution when I precipitated the gold with SMB, but I was wrong, the contaminant precipitated along with the gold, now it too has that shiny surface, although the color changed.
Concerning the gold shot, I tried a couple things to see what might happen to this mirror-like contaminant which seems to be mostly on the surface, but to no avail. I put some shot in nitric and nothing happened, I also tried melting some and adding sodium nitrate, again nothing. Strange that the contaminant would've been dissolved and in solution when I did the silver with nitric, then again in solution when I did the gold with aqua regia, both solutions having been filtered and crystal clear before precipitation. Now I get absolutely no reaction, yet the contaminant was in solution twice before, I don't get it..
There's a couple things which may or may not have meaning, both the gold shot and the silver are distinctly more difficult to melt than any I've done before, and they have a tendency somewhat to want to stick to my crucibles when fully molten and slipping and sliding around, in other words the molten beads get hung up in my ceramic crucibles, I never had these problems before and thought they might suggest contamination with palladium, yet from what I've read, SMB doesn't precipitate palladium out of aqua regia. Just to be clear, I never use my gold crucibles to melt silver, or for that matter, to melt any other metal other than gold, and the same goes for my crucibles designated for silver only, so contamination from the crucibles is out of the question.
Besides palladium, I considered platinum, but this didn't show up as a residue in any way shape or form when I originally dissolved the jewelry in nitric. I would think I'd see at least a trace of some sort of stubborn to dissolve metal in the sediment, whether it be palladium, platinum, or any other PGM, but there was absolutely nothing, all metal ended up in solution. Just to be clear, I didn't make shot out of the jewelry, I dissolved it as it was, simply cut it up as best I could and removed any iron such as springs, so I would think if one piece had managed to escape my notice and be made out of one of the PGM's, then I would expect that it would've been laying at the bottom whole, not affected by the straight nitric I was using, but nothing of the sort happened.
Just so you guys know, I use as little nitric as I possibly can, whether it be when working with silver and using only nitric, or when working with gold and using aqua regia at a proportion of 4 to 1. I always over calculate the amount of hydrochloric and under calculate the nitric. On top of that, if the under calculated amount of nitric ends up say for example to be 100ml, I use 40ml to start off, then go in increments of 50% of the last, thus the second addition is 20ml, always waiting till reactions subside before the next addition. Also, I never skip the addition of sulphuric, nor the evaporation step before precipitation, and I always filter and be sure make my solutions crystal clear. Just trying to give you guys some sort of idea that I've done this stuff before, with awesome results, until now.
It's interesting that whatever the contaminant is, it leaves the silver the same color as it should be, silver, yet the surface of the gold is turned orange, and by the way, the aqua regia was orange, not yellow or red, but right in between, orange. In the image you can see that the contaminant looks to be pretty much be on the surface, the biggest gold shot piece in the center has surfaces that are yellow as they should be, and surfaces that are orange covered. One last thing, when the gold was molten, there was no contaminants dancing around on the surface, the whole ball was exactly the same, like a mirror, they way it usually looks when I melt gold I've refined. Another indication that the contaminant is only superficial, thus only traces and not even 1% of the total weight, is that my original estimates concerning what I'd be ending up with where pretty much right on, the gold I got is pretty much exactly what I expected.
So I hope I've given a good enough idea of what I've encountered, does anyone have any idea what my contaminant might be and how to deal with it? Thanks.
I processed 395 grams of miscellaneous silver jewelry from the 60's and 70's (my mom cleaned out her jewelry box) using nitric and copper to do the precipitation. The shot I produced is silver in color like it should be and always is, however it's shiny, kind of mirror-like. The thing is, I then inquarted some gold with this contaminated silver, figuring the contaminant would remain in solution when I precipitated the gold with SMB, but I was wrong, the contaminant precipitated along with the gold, now it too has that shiny surface, although the color changed.
Concerning the gold shot, I tried a couple things to see what might happen to this mirror-like contaminant which seems to be mostly on the surface, but to no avail. I put some shot in nitric and nothing happened, I also tried melting some and adding sodium nitrate, again nothing. Strange that the contaminant would've been dissolved and in solution when I did the silver with nitric, then again in solution when I did the gold with aqua regia, both solutions having been filtered and crystal clear before precipitation. Now I get absolutely no reaction, yet the contaminant was in solution twice before, I don't get it..
There's a couple things which may or may not have meaning, both the gold shot and the silver are distinctly more difficult to melt than any I've done before, and they have a tendency somewhat to want to stick to my crucibles when fully molten and slipping and sliding around, in other words the molten beads get hung up in my ceramic crucibles, I never had these problems before and thought they might suggest contamination with palladium, yet from what I've read, SMB doesn't precipitate palladium out of aqua regia. Just to be clear, I never use my gold crucibles to melt silver, or for that matter, to melt any other metal other than gold, and the same goes for my crucibles designated for silver only, so contamination from the crucibles is out of the question.
Besides palladium, I considered platinum, but this didn't show up as a residue in any way shape or form when I originally dissolved the jewelry in nitric. I would think I'd see at least a trace of some sort of stubborn to dissolve metal in the sediment, whether it be palladium, platinum, or any other PGM, but there was absolutely nothing, all metal ended up in solution. Just to be clear, I didn't make shot out of the jewelry, I dissolved it as it was, simply cut it up as best I could and removed any iron such as springs, so I would think if one piece had managed to escape my notice and be made out of one of the PGM's, then I would expect that it would've been laying at the bottom whole, not affected by the straight nitric I was using, but nothing of the sort happened.
Just so you guys know, I use as little nitric as I possibly can, whether it be when working with silver and using only nitric, or when working with gold and using aqua regia at a proportion of 4 to 1. I always over calculate the amount of hydrochloric and under calculate the nitric. On top of that, if the under calculated amount of nitric ends up say for example to be 100ml, I use 40ml to start off, then go in increments of 50% of the last, thus the second addition is 20ml, always waiting till reactions subside before the next addition. Also, I never skip the addition of sulphuric, nor the evaporation step before precipitation, and I always filter and be sure make my solutions crystal clear. Just trying to give you guys some sort of idea that I've done this stuff before, with awesome results, until now.
It's interesting that whatever the contaminant is, it leaves the silver the same color as it should be, silver, yet the surface of the gold is turned orange, and by the way, the aqua regia was orange, not yellow or red, but right in between, orange. In the image you can see that the contaminant looks to be pretty much be on the surface, the biggest gold shot piece in the center has surfaces that are yellow as they should be, and surfaces that are orange covered. One last thing, when the gold was molten, there was no contaminants dancing around on the surface, the whole ball was exactly the same, like a mirror, they way it usually looks when I melt gold I've refined. Another indication that the contaminant is only superficial, thus only traces and not even 1% of the total weight, is that my original estimates concerning what I'd be ending up with where pretty much right on, the gold I got is pretty much exactly what I expected.
So I hope I've given a good enough idea of what I've encountered, does anyone have any idea what my contaminant might be and how to deal with it? Thanks.
