Johnny Williams said:
First of all let me say, “ some people look like their pet”, and others, think like their pet.
To begin: The Ag is plated out of a fixer solution from an x-ray operation. Using a vintage x rite recovery system. Basically the Ag is plated on to several circular disk (stainless steel) and removed. When the Ag is remove, junk also is noted .The Ag is not shinny, other material in the fix, is deposited along with the Ag. By dissolving in HNO3 and filtering, the plated Ag should clean up. The copper tubing placed in this sol, Cu taking the place Ag in the silver nitrate, with Ag metal dropping out. Gold silver pro, does this help? I have noticed that a copper tie off used in GC work, drop a material that come together and not the cement looking stuff .The copper source (GC column tie off that are made of copper not the ss ones), had to be shaken to remove the material that precipitated on to it. I don’t need any more of a mess then I all ready have.
It didn't need "cleaning up".
When silver is plated out of fixer, it can look, at worst, like a black (sulfide) slimy stinking mess and, at best, a hard, thick, brittle, fairly bright, silver color (As plated, the silver will never be pure and will always contain some sulfur, as sulfides. This is what makes it brittle. At best, it will only be about 98% pure). Usually, it's somewhere in between the 2 extremes. The condition of the deposit is dependent on several variables - current density, concentration of silver in the solution, etc. However, no matter how it looks, there are no other metals contaminating it. The silver originally on the film was near 99.99% pure and no metallic contamination was introduced by the fixer or the other chemistry. Therefore, all you had to do to get a pure (at least 99.9%) silver bar was to first dry it and then melt it properly. It's a very simple process, if you have a crucible furnace. Although iron (rebar) is used in the process, it won't significantly contaminate the silver, if done properly.
When you dissolved it in nitric, you made the situation much worse and created a lot of extra work. First, by doing this, you may not get it all. Second, by cementing the silver from the nitric on copper, you are contaminating it and about the best final purity you can hope for is 99%. Third, you have essentially wasted nitric and copper, both of which are expensive.
Here's how the direct melting is done:
(1) Dry out the material. A stainless pan on a hotplate will work. Just dry it, don't burn it. Do this outside or under a good fume hood, since the sulfurous fumes coming off really stink.
(2) Crush up the dried material a bit and blend it with about an equal volume of borax, if you're using common borax. Common borax (Na2B4O7.10H2O) contains about 47% water and will expand enormously when melted and can flow over the top of the crucible. Anhydrous borax (Na2B4O7) is best since it contains no water and won't expand. Also, when using anhydrous borax, you can get away with using about half as much. The common borax is much cheaper and will work fine. You just have to be more careful to prevent foamovers.
(3) If common borax is used, fill a warm crucible about 1/3 full with the mix. If anhydrous borax is used, you can fill the crucible about 1/2 full. Place several lengths of rebar in the crucible. The rebar should be long enough to stick out of the crucible at least 4". That way, you can easily remove the rebar before pouring the melt. The sulfur in the material (the black stuff) will combine with the iron from the rebar, forming iron sulfide, and this will enter into the slag. In simple terms, the iron pulls the sulfur out of the silver and purifies it. When you pull out the rebar, you will see that it's been partially eaten away.
(4) After the charge is molten, let it dwell at that heat for about 15-20 minutes, stirring occasionally with one of the pieces of rebar.
(5) Remove the rebar. Pour the molten metal/slag into a preheated cast iron mold. To act as a mold release and prevent the welding of the silver to the mold, the mold should first be carboned before pouring. The easiest way to do this is to coat the inside with WD40 or brush on a layer of motor oil - there should be no puddles. You can also coat the inside of the mold with carbon by using the flame from an acetylene torch - use acetylene only - no oxygen.
(6) When it has all become solid, dump it out of the mold. When nearly cool, break off all of the slag from the bar, using a hammer or whatever it takes. Sometimes, if you set the bar on its side and strike the interface with a hammer, where the slag meets the silver, the slag will come off cleanly. Some like to turn it upside down on a steel plate and pound on the bottom of the silver. Some quench the still hot bar. To get the last traces of slag, some hold it under a faucet and tap the remaining bits with a welder's chipping hammer. Whatever you do, get all of the slag off the silver. Buyers don't pay silver price for slag.
(7) After slag removal, the bar may not look that great. You might want to remelt it.
(8) Weigh the pure silver bar.
Note: This method only works well with a gas-fired crucible furnace. I can't see how one would do it in a torch melt. Manipulating the rebar would be too cumbersome in an electric box furnace. I guess you could put small chunks of iron in the crucible but it would probably be more difficult to convert all of the sulfur to iron sulfide that way. By using rebar and stirring it occasionally, all of the sulfur will eventually come in contact with the iron and be converted.
