# Gold/Silver Ingot Casting HELP NEEDED!



## youngling (Jun 19, 2016)

Hello fellow GRF members,

Being new to the world of metals refining , i had no idea where to start and finding this Forum was a blessing. This forum is literally a Gold Mine! Special Mention and Thanks to lazersteve and Harold_v!!

i am currently in the process of fine-tuning the casting operations at work and was looking for guidance and pointers in the Casting department.

i am currently using a 5kg induction furnace with graphite crucible.
i usually cast 700gm ingot bars in a open mould made out of Cast Iron.
i use a Silicone mould release spray to lubricate the mould before each pouring.
i also make sure i pour under a reducing flame with LPG Gas(butane+propane)
I use Ammonium Chloride & Borax as flux,if needed.

I've had all kinds of problems , i thought i would organise all my doubts and post them in one go! :

Is it necessary to have a flame over the crucible while the gold melts?i read that this prevents the metals from being oxidised(esp Silver), however I've had people tell me that it is unnecessary. i tried it and could not find any improvements in the casting.I am just learning that silver and gold behave differently, could someone explain?

After the gold has been throughly melted, the crucible is carried over to the casting tray where the mould is kept,i find that streaks of oxidised gold forms on the molten mirror like surface of the gold while it is being carried to the mould.this in turn flows out and come on top of the ingot,pictures are attached below….is this oxidised gold? or is it due to some sort of chemical lingering on from the AR process? I've been doing all sorts of things to get rid of it, any suggestions on eliminating this streak/stain ??



I have come to realise that controlled cooling is very much important to get a mirror like surface finish on the bars, I'm in the process of devising a cooling plate for this. is it worth getting a cooling plate? and could i get any tips on how to improve surface finish and reduce casting defects like Rings and piping ?

After the ingot has been casted , i quench it in a tub of ammonium chloride solution and then water, is this advisable ? is there a better method of doing it ? this has been the age old practice of the company i work for.

While casting 9999 electrolytic silver, even though i cast it under a reducing flame .sometimes i get these black scabs forming on the surface of the bars(pics Below), what are they ?any remedies ?



I am just starting to learn about casting - any sort of ideas, suggestions,criticisms are welcomed.
thanks,
youngling

moderator please feel free to edit my post as you deem necessary.


----------



## Palladium (Jun 19, 2016)

If those are pure metals you need no flux. It looks like flux residue to me. Try putting the gold in 25% nitric and giving it a good boil. That should remove the flux without any scrubbing so as not to scratch up the bar surface. For the silver try a boil in diluted sulfuric to remove the flux. Are your using a clean crucible to start out with or one that may have had trash in it from a previous melts. Once you start using the crucible for melting only use it for pure metals and once it starts to become dirty then you can still use it to melt up your anode bars in.


----------



## youngling (Jun 19, 2016)

@palladium - yea you maybe right, ive been using the same crucible for both impure and pure silver melts, thanks- that was stupid of me.sometimes its the easiest things that make the difference 

the funny thing about the "stain" on the gold bar is that, while it is in the furnace there isnt a single "stain" on the molten gold surface, its clear and mirror like....but as soon as i take it out and proceed to pour , these "stains" form and flow out into the mould. somehow i have a feeling its not flux,because its part of the gold.and i do get bits of flux once a while,heres another bar with a larger stain - 
.
ive been trying to solve this for over a month with no result, my best guess is that they form due to oxidation and drop in temperature.i even thought id use the tilting feature of the furnace inorder to maintain the same temperature while casting , but we've never done this and terrified that well end up loosing metals due to spills 

I am relatively new to casting,and have much to learn . thanks again palladium


----------



## etack (Jun 19, 2016)

Have you XRFed it to see whats your contamination? It looks like Pd might be your problem. Its not the cooling or the melting its the refining.

Eric


----------



## Lou (Jun 20, 2016)

PGM contamination, or Se/Te or something like that. You need to refine it better. No reason why your gold or your silver should look like that. Black on the silver is iron contamination.


Lou


----------



## upcyclist (Jun 20, 2016)

Lou said:


> Black on the silver is iron contamination.


Youngling, you mentioned cast iron ingot molds. Have your molds started scaling at all? Might you consider moving to graphite?


----------



## g_axelsson (Jun 20, 2016)

youngling, how did you refine your gold and silver?

As several experts already pointed out your gold and silver contains some contamination. Gold and silver doesn't oxidize but contaminants can. Your graphite crucible is creating a reducing and oxygen free environment so contaminants could stay metallic. When exposed to air it will oxidize rapidly, showing up as floating blobs on the molten gold.

Fine silver won't oxidize but can absorb a lot of oxygen and when it is solidifying the oxygen will create a lot of bubbles on the surface, giving it a porous appearance.

A good example of casting a silver bar by one of our regulars : https://www.youtube.com/watch?v=bEGkoTc17Zw
And another one of casting gold bars : https://www.youtube.com/watch?v=HX1ej0PAhYQ
As you can see, the surface turns into a mirror when it solidifies, although there are something on top of the silver bar in that video.

Göran


----------



## youngling (Jun 20, 2016)

etack said:


> Have you XRFed it to see whats your contamination? It looks like Pd might be your problem. Its not the cooling or the melting its the refining.
> 
> Eric


hmm, im gonna XRF the scab tommorow, will post the results tommorw. will be on the look out for PGM's. thanks eric


----------



## goldsilverpro (Jun 20, 2016)

I think the first thing I would do is switch to a graphite mold.


----------



## youngling (Jun 20, 2016)

upcyclist said:


> Lou said:
> 
> 
> > Black on the silver is iron contamination.
> ...


I have a couple of moulds on stand by ,I alternate between them to prevent scaling.nothing as of now .we keep them clean and maintained either with carbon soot or silicone mould release spray.
I did try graphite Moulds , but found them uneconomical...they deteriorate too fast.or maybe I've been storing it wrong.
are you using graphite? how long do they last?
thanks lou


----------



## youngling (Jun 20, 2016)

g_axelsson said:


> youngling, how did you refine your gold and silver?
> 
> As several experts already pointed out your gold and silver contains some contamination. Gold and silver doesn't oxidize but contaminants can. Your graphite crucible is creating a reducing and oxygen free environment so contaminants could stay metallic. When exposed to air it will oxidize rapidly, showing up as floating blobs on the molten gold.
> 
> ...


Goran, the gold was done using Aqua Regia, and silver through Electrolytic. i am yet to enter the refining part of operations here :| . so i cant really tell you how it was done,but ill get back to you ASAP.


----------



## youngling (Jun 20, 2016)

So i should try changing the mould. And check for PGM or Te/Se contamination. I'm going to XRF the bars tomorrow,and see if its contaminated- it makes sense,its most likely,that. thanks guys...this information has been priceless. will post more info tomorrow.


----------



## Palladium (Jun 20, 2016)

What type of process are you using for the silver? Just dissolve and cement or are you using a chloride conversion using iron and sulfuric and then a cell to clean it up. Is the silver from jewelry or another source? I have graphite molds that i have used for no telling how many lbs of silver and they still look good except for the damage from dropping or where i grab them with tongs. I was looking at the pics with my phone, but now that i look from my laptop it does look like iron and some pgm contaminates on the silver.


----------



## Lou (Jun 20, 2016)

I actually use all cast iron molds for anything over 50 ounces troy--silver and gold. I'm not going to argue that graphite makes a better product--but I don't really care (nor do the consumers) what it looks like on the big ones because they just get remelted and made into stuff anyway. I dress 'em with acetylene soot and preheat them til spit won't stick and cast into molds put upon a 1/2" X 24X 26" copper plate on a 150 lb block of aluminum.


Unless you have a very nice XRF, it'll be difficult for you to see the impurities discoloring the gold. Looks like overuse of SO2 to me. 


FYI, the flame over the mold is useful but only if you have the proper fan flame. Silver doesn't oxidize, nor gold; it's the other crap that can give it the pea cocking or crabbing. There are ways to address that...

Anyway, the likely culprit is silicone mold release. Stop that. Soot. Use soot. Nothing better. I still soot graphite if I want that fine finish.

Lou


----------



## upcyclist (Jun 20, 2016)

Lou, I love your mix of good lab protocols, scalability, and pragmatism: 



Lou said:


> I dress 'em with acetylene soot and preheat them til spit won't stick


----------



## Lou (Jun 20, 2016)

Figured I'd save everyone some time rather than say "til a drop of saliva undergoes the Liedenfrost effect''. I think most everyone here's spit on something really hot before and seen it skitter around. That's what you want if you don't want your bars piping on you, more so on the smaller molds.

Lou


----------



## MGH (Jul 20, 2016)

Also... I've got acetylene. I've got spit. I could probably find a big copper plate. Now where did I leave my 150 pound block of aluminum :shock: 

Nonetheless, I too always enjoy reading these kinds of posts that can only come from experience.


----------

