Non-Chemical Bar Finish

[Topher_osAUrus]

I resent that last gold piece to be of any purity, it's appalling and a really bad refining with palladium or iron as possible contaminants.

Oh, hush!

That nugget of yours was beautiful! The fern patterning from Pd is beautiful in its own right!

But, I know the feeling, and can agree to an extent, that you cannot really beat that mirror finish that pure, I mean really pure gold has.

Just dont be so hard on yourself Göran!

 

[g_axelsson]

Sorry, forgot the smiley. :mrgreen:

Göran

 

[Lightspeed]

Some more info here with a few links within the thread:

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?t=3710

I think a major problem with what you are trying to achieve is the size of the melt, eg: more metal=longer melt time/cooling= more oxygen absorbed on heating then expelled on cooling.
You have stated you have achieved this at home with smaller bars, there are also examples from members here on Youtube displaying their method.

I don't really have much more to offer as I have never tried that size pour with the finish you want to achieve. Short of using a cast ingot mold and sprinkling borax over the exposed surface after pouring, then a pickle.

here is a similar furnace to the one I have seen commercially used to produce the quality you are trying to achieve in finish. The metal is melted in situ inside the graphite mold. You may be able to research the procedure/method of these furnaces, but then applying that at home may simply be impossible or not economically viable or just plain out of reach. I have seen single bar units that do the same job but again these are commercial units.

http://www.italimpianti.it/en/tunnel-furnace-gold-silver/

My conclusion is that if it were that simple to do, then commercial refineries would not be using complex systems such as these to attain the desired end product.

 

[autumnwillow]

A cheat! Get a buffing wheel and polish with red rogue. No crystal like patterns though but you will have that lustrous finish. It is how heraeus makes their fine silver bars after stamping.

 

[Palladium]

A cheat! Get a buffing wheel and polish with red rogue. No crystal like patterns though but you will have that lustrous finish. It is how heraeus makes their fine silver bars after stamping.

That's sort of like having sex with a condom on ain't it? :mrgreen: :mrgreen: :mrgreen:

 

[colu41]

So I decided to give it one last pour. And got this.

https://flic.kr/p/XCAbNo

It started cooling perfectly, until the very end and it spit and spattered like crazy. Its about 6 grams overweight, so I may just tumble it in some stainless polishing media, stamp it and call it good. I think this will be my last bar of this size . Going to stick to 5 and 10 oz.

 

[colu41]

I had a new idea. I'm wondering if anyone has ever tried this. With the bar I have, what would happen if i just heat up the top of the bar with a torch for a bit, would it possibly smooth out the bubbles without having to remelt the entire bar again?

 

[cosmetal]

I'm still a noob to PM refining but not to metal casting, etc.

Personally, I don't think you would be happy with the results. With a torch applied to the top area only, the whole bar will be acting as a heat sink and the heat affected zone will probably end up as a crater instead of your desired uniform surface.

But, if you are going to remelt anyway, why not try it and post pics of your results. You never say "never".

 

[g_axelsson]

So I decided to give it one last pour. And got this.

https://flic.kr/p/XCAbNo

It started cooling perfectly, until the very end and it spit and spattered like crazy. Its about 6 grams overweight, so I may just tumble it in some stainless polishing media, stamp it and call it good. I think this will be my last bar of this size . Going to stick to 5 and 10 oz.

If the silver is spitting and frothing when it cools it is because you have dissolved oxygen in the silver. Try remelting it under reducing conditions and not oxidizing. If you melt it in a furnace you could try to add a couple of pieces of charcoal on top during the melt. The carbon will react with the oxygen and keep the atmosphere in the crucible oxygen-free.
If you look at videos of people pouring silver they usually have a rich flame covering the surface of the mold. The flame is usually quite yellow, hinting about a rich reducing flame.
The longer the silver stays molten the more oxygen it can absorb, so a quick melt and pour also reduces the amount of oxygen that is absorbed.

This is a good example on how to do it.
https://www.youtube.com/watch?v=bEGkoTc17Zw

Göran

 

[Topher_osAUrus]

Some books say to have a piece of charcoal in the crucible while melting to keep the oxygen from being taken up by the silver.

Never tried it, as i sell my crystals, but i found it interesting

 

[colu41]

Interesting. I may just try the charcoal trick. How much are we talking here? I work at a carbon plant so, I could take whatever I need but, would it just be a little spoonful or a pinch? I'll try anything at this point for a decent looking bar.