# Gold and silver bullion



## elfixx (Mar 13, 2009)

Just a few bar :wink:


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## Noxx (Mar 13, 2009)

You used a graphite mold, did you ?


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## elfixx (Mar 13, 2009)

Only for those silver bar, I cast my gold bar using a adjustable steel mold.


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## Noxx (Mar 13, 2009)

Oh, that's great to know that steel molds give that finish on the ingots.

What's the thickness of your gold ingots ?

Thanks


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## elfixx (Mar 13, 2009)

Just a few millimeter thick, about 4mm.


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## Anonymous (Mar 13, 2009)

What are the clear sparklelys besides the bars?


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## elfixx (Mar 13, 2009)

Those are some stones such as diamond, cubic zircona as well as a small ruby and saphire


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## JustinNH (Mar 13, 2009)

looks great :wink:


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## Oz (Mar 14, 2009)

I have to ask what are you guys doing to get those concentric rings in those bars with a graphite mold. All that makes sense is that once poured you are playing a torch over it to smooth it and slow the cool, which will play havoc with your graphite. Having said that I have never tried a graphite mold but understand why you want it to cool slowly.


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## Noxx (Mar 14, 2009)

It cools so fast that it makes concentric rings. When pouring very small ingots, gold solidifies as soon as it touches the mold.

Graphite is very heat conductive.


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## Oz (Mar 14, 2009)

Do you not start with a warm mold?


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## Harold_V (Mar 14, 2009)

Noxx said:


> It cools so fast that it makes concentric rings. When pouring very small ingots, gold solidifies as soon as it touches the mold.
> 
> Graphite is very heat conductive.


Yep! The prettiest ingots I poured, and it was consistent----were the ½ ounce size. By preheating the mold, blackening well with a sooty acetylene torch, and pouring fast, then applying a reducing torch to slow cooling, I ended up with perfect little "loaves of bread" with no shrink rings or sharp edges. I poured to an iron mold. I expect graphite would be quite difficult.

Something to consider. Soot is made of a lot of dead air space. Unlike graphite, it does not conduct heat well. One might consider blackening a graphite mold to see if it makes a difference in freeze rate. 

Still, nice ingots, Noxx. The color is spectacular. You are doing your work well. :wink: 

Harold


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## goldsilverpro (Mar 14, 2009)

> One might consider blackening a graphite mold to see if it makes a difference in freeze rate.



I don't know about the freeze rate, but it can definitely improve the appearance of the ingot.


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## Noxx (Mar 14, 2009)

I don't have an acetylene torch so I can't tell...

But, since you said that a blackening coating (soot) consists of small air «bubbles», I suppose the resulting ingot will not have that nice mirror finish ?


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## qst42know (Mar 14, 2009)

If the corners of your mold aren't to sharp you may try a kerosene lamp flame to soot your mold. It wouldn't be as effective as an acetylene torch but may be an improvement.


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## goldsilverpro (Mar 14, 2009)

I usually sooted the graphite silver book molds. The silver came out noticeably more bright, shiny, and smooth.


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## elfixx (Mar 14, 2009)

Hey noxx I noticed the bar you casted using the same type of graphite mold as me shows no bubble or cavity on the bottom side how did you do that? My bars always have bubble shape cavity even when heating the mold to around 1100 C.


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## Harold_V (Mar 14, 2009)

elfixx said:


> Hey noxx I noticed the bar you casted using the same type of graphite mold as me shows no bubble or cavity on the bottom side how did you do that? My bars always have bubble shape cavity even when heating the mold to around 1100 C.


That may be your problem. When you heat graphite to the point of ignition, it produces carbon dioxide, which is likely what is creating the gas pocket. Try heating to a lower temperature (under 1,000° F) and blacken the mold with a smoky torch. There's a delicate balance of freezing rate where the gold will freeze without forming rings, and not create the gas pocket. 

Playing a reducing flame on the surface after casting the gold can slow down cooling such that you can eliminate the pipe and radical shrink. Controlled cooling will allow the entire ingot to shrink as it solidifies.

Casting ingots is truly an art. I never mastered it to my satisfaction. 

Harold


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