# Bar Finish



## colu41 (Sep 17, 2017)

So its been awhile since I've made any silver bars for myself. But now I'm back into it. And a little more serious about it. Two years ago I started a small knifemaking business, so I built myself a small high temp oven/kiln for heat treating. And now it doubles as my melting furnace.
My question is.
I've melted this 500 gram bar 3 different times with slight changes in the process. I'm looking for the smooth top look, like the Perth Mint, or the RMC poured bars. I'm not a HUGE fan of the thick pour lines, and the deep trench in the middle is just unattractive. Here is my last pour. The silver itself was heated to 1975* F in the furnace. And then poured into a warmed graphite mold. A Mapp torch was over the pour the whole time, hoping to eliminate as much of the excces O2 as I could. Could someone give me some tips on how to get the look I'm going for? I've never done a pour this big before either. I've only really done, 1 through 5 oz pours in the past.

Thanks!

https://www.flickr.com/gp/[email protected]/8gfHqv


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## Palladium (Sep 17, 2017)

Are you only pouring 1 single 500 gram bar or are you pouring multiple bars?


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## colu41 (Sep 17, 2017)

One single 500 gram bar. Link to the pic is my OP


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## Palladium (Sep 17, 2017)

Looks like you still have oxygen. The mapp torch uses ox to burn and is pouring it into your silver as it cools. Trying using just pure propane gas burning and feed from a bbq grill tank burning over the top of it. If it's only one bar put it back into the mold and melt it and the mold at the same time in the furnace. Turn the furnace off and let it cool down for about 15 minutes and then remove the bar. Controlled cooling is the key, but your still not going to get a perfect mint bar.


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## colu41 (Sep 17, 2017)

I did not know that Mapp uses oxygen. Next melt I'll just use a straight propane tank and see if there's a difference.
And are you suggesting remelting the bar right in the graphite mold? I've always been told that isn't good for the mold but, worth a shot maybe for last resort.

I understand I won't get the quality of say an induction style pouring system or whatever those cool machines are but, smoother than I currently am doing.

When I was doing smaller bars they were turning out great, decently smooth, clean and with a lot of luster. These bigger bars seem to bubble a lot more and leave the finish a little matte colored. 

Thanks. I'll try to post some more pics tmrw when I try the propane.


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## Lou (Sep 17, 2017)

Kilo done with H2 fan flame


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## Topher_osAUrus (Sep 17, 2017)

Lou said:


> Kilo done with H2 fan flame



Show-off. :wink: 
Kidding, of course. I myself, very much appreciate seeing pictures from the guys who have been doing this and doing this, and doing this well.


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## colu41 (Sep 17, 2017)

I'm not even sure what this H2 Fan Flame even is. How is that done?


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## Lou (Sep 18, 2017)

Here's a good article.


http://www.legor.com/uploads/asset/file/351/LorisCuman_EN.pdf


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## colu41 (Sep 18, 2017)

So this process is just essentially putting the metal in the mold and running it through an electric oven with 100% time & temp controllability. 
Aren't the graphite molds very susceptible to wear and breakage when heated up repeatedly and for long periods of time?


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## Palladium (Sep 19, 2017)

I once had 5 plates made that had 10 1 oz cavities each = 50 bars. You need PURE silver. I used the cell followed by a cl step. The client wanted 1,000 bars back. He sent me the silver brazing to refine and then wanted something special back. He's a long term investor and just wanted something unique back. Money wasn't his thing, he had plenty of that! Must be nice right! lol He didn't want the average of what everybody else wanted like flat and smooth. It was the snowflake crystal pattern he was after. Yawl know the ones i'm talking about!

I made the mistake of sending him one back from his lot that came out just right! He paid for the molds and everything i requested. It cost several hundred dollars! He explained it to me like this. He said i only lose money based on today! He said it's a 1,000 oz and if it cost me an extra dollar an oz do you think i'm going to worry about it? Tomorrow it will go up that dollar and i will still make money. Anyway i handled the mold with kid gloves and they held up just fine as far as i'm concerned. New molds, pure product, NO flux!


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## Lou (Sep 19, 2017)

In case y'all didn't know, this is what the crystal pattern he's talking about looks like.


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## Lou (Sep 19, 2017)

colu41 said:


> So this process is just essentially putting the metal in the mold and running it through an electric oven with 100% time & temp controllability.
> Aren't the graphite molds very susceptible to wear and breakage when heated up repeatedly and for long periods of time?



No. Not really. It is very high density graphite and in protective atmosphere.

For you, fan the still molten metal with a billowing reducing flame to prevent the contraction marks. Also, preheat mold.


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## colu41 (Sep 19, 2017)

Well, thanks for the help guys. I tried this multiple different ways again. Pouring it with a light propane flame on it to reduce O2. I tried a warm mold. And I tried a hot mold.
Then, I put the bar back in the mold, and put it in the furnace. Covered it with another piece of graphite, and let her cook for about 15 minutes at 2050*.
And it turned out like this...

Heres a direct link. https://flic.kr/p/YC2pfU
It still has a very deep hole in the center. The lines I guess are not the same as a hand pour but, it looks and feels like sandpaper. The bottom of the bar is very defined and smooth. Just has a matte silver color to it. I just can't seem to get this anywhere near what I'm looking for and I've tried almost everything.
I may just do one last hand pour and go for no bubbles, and deal with the pour lines. But even trying to get no bubbles on this large of bar seems impossible for me.﻿


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## Palladium (Sep 19, 2017)

How are you controlling the cooling rate? Did you just pull it out and let it cool with the other graphite on top?


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## Lightspeed (Sep 19, 2017)

I thought I had already posted this before, don't know where it went so......

Commercially I have seen the melt process of gold and silver bars from refined metals when a mirror surface finish is desired. The refined material is placed into a graphite mold and covered with a graphite slab as stated above, this mold is then forwarded into an electric tunnel furnace which uses a controlled atmosphere in both the melt and cooling phases.

There is one thing you could try as they also use it commercially, that is placing a graphite slab cover over your mold to minimize and aid in keeping a reducing atmosphere when the bar is in the melt stage and then during the cooling process, the bars from this procedure come out with a mirror finish, the atmosphere and cooling time needs to be controlled though, as the above posts have indicated.


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## Palladium (Sep 20, 2017)

Some eye candy from the library!


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## Palladium (Sep 20, 2017)

Au !


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## g_axelsson (Sep 20, 2017)

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.

After a second refining with an inquarting step added it got a mirror finish.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=19840#p236805

Göran


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## colu41 (Sep 20, 2017)

After the melt period, I turned the furnace down about 500 degrees every 5 minutes. And after 10 minutes it was at about a 1000*, I shut the furnace off and let it sit another 10 minutes. The mold was covered with graphite. and I dont know how much more control I can get from that.


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## Topher_osAUrus (Sep 20, 2017)

g_axelsson said:


> 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!


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## g_axelsson (Sep 20, 2017)

Sorry, forgot the smiley. :mrgreen: 

Göran


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## Lightspeed (Sep 20, 2017)

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.


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## autumnwillow (Sep 21, 2017)

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.


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## Palladium (Sep 21, 2017)

autumnwillow said:


> 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:


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## colu41 (Sep 21, 2017)

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.


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## colu41 (Sep 23, 2017)

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?


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## cosmetal (Sep 23, 2017)

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".


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## g_axelsson (Sep 23, 2017)

colu41 said:


> 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


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## Topher_osAUrus (Sep 23, 2017)

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


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## colu41 (Sep 24, 2017)

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.


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