# need help melting silver



## azdave35 (Oct 27, 2011)

we have about a pound of refined silver we want to melt and pour into a cone mold..after pouring it into the preheated mold and letting it solidify we dump it out of the mold...it is full of big pits and holes..has anyone experienced this ?...any advice?..thanks in advance


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## philddreamer (Oct 27, 2011)

Pure silver absorbs oxigen, so if you used a torch with oxigen that's most likely the reason for the pits. 
Take a look at this video, it shows Peter (Kadriver) pouring some fine looking silver ingots.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=11783

Take care & be safe!

Phil


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## MysticColby (Oct 27, 2011)

what was mold material? could be it wasn't heated enough to get all the moisture out (plaster needs to be heated to about 500 C over 6 hours to remove all the chemical water. better investment materials (Americast, for example) should probably be done hotter/longer to ensure 100% water removal (they can be heated hotter and longer, while plaster will start crumbling)
other option is that the silver wasn't hot enough and/or mold wasn't hot enough, and the silver solidified before it filled the mold. plaster can't be too hot when removed from meltout kiln; maybe 150 C. better investment can be upwards of 500 C when poured. silver melts around 960 C, but should be hotter when poured into mold, say 1200 C


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## azdave35 (Oct 27, 2011)

hi guys...i was using a propane furnace made for melting gold...it fires at over 2000 degrees f...the mold is a steel mold


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## philddreamer (Oct 27, 2011)

Dave, could you share some pic's? Maybe someone could "see" some clue.

Thanks!


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## azdave35 (Oct 27, 2011)

maybe this will help


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## Palladium (Oct 27, 2011)

That's refined silver?


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## azdave35 (Oct 27, 2011)

not much of a pic but its the best i could do with my camera


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## element47 (Oct 27, 2011)

This is a physical characteristic of the element Silver. In its plastic zone, the temperature area just before it liquifies, going from cold to hot, it absorbs oxygen. Going back from hot to cold, it gives up that oxygen. Silver can "spit" when it cools, but in any event, it gives up that absorbed oxygen and that is the source of those holes. Bubbles of gas given up. I am sure that a preheated ingot mold will assist in obtaining a better finish on the ingot, as it *might* help the silver stay liquid longer, but in the research I have done, I believe you have to take further steps than just preheating the mold. Silver usually freezes VERY quickly. 

Logically, the methods of reducing this effect would be:

a: hold the heat on the silver as it cools longer, allowing more time for more gas to escape while the silver is still limpid, liquid-like. I think you'll see kadriver do this in his videos. 
b: perform the melt in an oxygen-free atmosphere. 
c: use a reducing flame to reduce the amount of oxygen the melt gets exposed to. Kadriver does this, as well.


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## azdave35 (Oct 27, 2011)

thanks for the info...that sounds like what is going on...the only thing is i am using a propane furnace ..not a oxy-acet torch...anyone have any advice on using the furnace with better results?


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## philddreamer (Oct 27, 2011)

Thanks Element!

Dave, what is the source of the silver, & which process did you use for refining it?

Phil


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## azdave35 (Oct 27, 2011)

the silver comes from jewelry...it was digested in nitric and distilled water and cemented out with copper


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## element47 (Oct 27, 2011)

I don't know this for certain, but it may well be that you cannot get a sufficiently reducing flame with a propane furnace to avoid this oxygen uptake. It depends upon how well you can control the air entering the furnace. It also depends if you are heating the crucible in the propane furnace and then lifting it out to pour your ingot in open air. It may be that an excess of fuel will produce not enough heat to keep the silver molten. These things all interact. 

If you want to try, it makes sense that you are going to have to cut off part of the airflow to the area of combustion. OR, you have to substantially increase the amount of fuel injected into the furnace such that the proportion of air present in the area of burning is less. Not knowing the nature of your furnace nor the capacity of the valve on your fuel supply or regulator, I don't know if either (or both) of these are possible.


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## Palladium (Oct 27, 2011)

Looks like you have some copper in there.


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## MysticColby (Oct 27, 2011)

azdave35 said:


> thanks for the info...that sounds like what is going on...the only thing is i am using a propane furnace ..not a oxy-acet torch...anyone have any advice on using the furnace with better results?



You should have some sort of choke on the propane torch. Possibly not, but it's better to have one. If you restrict air getting into the furnace, the propane will consume all the oxygen when it burns, and then escape out of the furnace seeking more. Not the most efficient, but it does limit oxygen inside the furnace.


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## samuel-a (Oct 27, 2011)

Half a teaspoon of Flour added over the silver powder could keep a reducing environment inside the crucible.

To me, it seems that this silver blub is quite contaminated with Cu and not melted at high enough temp'... it takes only a fraction of percent of Cu to prevent the Oxygen absorption phenomenon of Ag.


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## qst42know (Oct 27, 2011)

Is this an open top crucible furnace?


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