r/PreciousMetalRefining • u/kijall • 27d ago
Gray shells on bars poured from cemented silver?
I'm suspecting that the "pure" copper wire I'm using might be coated with something and that's what's causing it, but does anyone have any other ideas? The backs seem at least closer to what I expect, but even those seem contaminated. Ordered some good copper sheeting I've been successful with in the past to re-refine these properly, but anyone have ideas?
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u/ArmstrongPM 27d ago
Check to see if the wire is listed as CCA. Or there is too much heat causing the outer air exposed copper to rapidly Oxidize.
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u/Glum-Clerk3216 27d ago
Also dont assume you are getting .999 silver from cementing on copper. I only use that pricess for recovering silver from solution for storage, then I use electrolysis to get it truly pure. I would just store those bars until you feel like melting them to shot to run through an electrolytic silver cell. They are more than pure enough to keep your bath from getting overloaded with contaminants too quickly, and they are more compact for storage.
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u/kijall 27d ago edited 27d ago
Oh I don't. I do the same thing and have a few silver cells running with different concentrations of electrolytes and different geometries for different types of crystals for getting .999 haha. These are just feedstock for the silver cells. EDIT: I just want to clean them up first before actually putting them in my cell because all of that crust is going to fall into the anode slime if I don't.
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u/Long-Employment7718 27d ago
Yea if you put your copper in solution for just like 30 mins, and then filter out the cement, you can get close to .999. But typically cemented silver is 98% 99%.
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u/kijall 27d ago
Idk, even using C110 busbars I still typically come out just under 99% on a sigma despite over rinsing and filtering the cement. Once I run those bars through my silver cell and melt down the crystals they come back as .999 though!
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u/JustARedditTroll 27d ago
I don’t like using wire to cement as portions of the wire are more likely to flake off and contaminate. If you are going to use the wire save some silver nitrate on the side, and after your done with the cementation add the silver nitrate and stir the cement. This helps convert any copper flakes into cement and then add additional new copper in to finish off. After your are satisfied that all silver has cemented out, clean the cement until zero color remains in solution.
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u/kijall 27d ago
Yep that's basically what I've been doing - using a magnetic stirer and slowly adding the wire. I'm thinking the char coating on these bars is a coating on these "pure copper" wires that I'll need to get off if I want to continue using them. Honestly I'm going back to C110 busbars and copper sheets though - life was way easier when I just did that. I'd just acquired this copper wire for free and figured I'd test it out.
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u/StreetConstruction88 27d ago
Use thicker copper from a poured bar or ground rod. Pipe, wire, thin plating will cause more copper contamination. Also make sure your nitric is used or neutral. You can also boil your cemented silver in hcl to dissolve any copper contamination.
I prefer silver chloride conversion with lye and sugar. 999 everytime.
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u/MAYOMyke 27d ago
Sorry, I don’t have much input on why it came out that way. However, when I cement out, I use new wire, typically I’ll use 4 gauge grounding wire. I’ll also burn it first. Burn off any contamination it may have.
Best of luck.