HOW TO CAST 1KG GOLD BAR

Shop deals on ebay
xelexo
Advertise with us
shop deals on amazon
Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Dr. Poe said:
In jewelry casting, the reddish surface coat is due to traces of copper contamination. The copper oxide is polished away with fine grit on a buffing wheel. In the South African Rand, ingots of gold are polished by a large flame from a torch immediately after pouring (while the ingot is still hot). The inner part of the flame is a reducing flame and robs the trace copper oxide of it's oxygen (removing the red hue). Sometimes the simplest answers are the best. Regards; Dr. Poe 8)
Click to expand...

Which gas is used oxygen, propane, argon, or nitrogen??
can u elaborate more
hrushi
 
Dr. Poe said:
In jewelry casting, the reddish surface coat is due to traces of copper contamination. The copper oxide is polished away with fine grit on a buffing wheel. In the South African Rand, ingots of gold are polished by a large flame from a torch immediately after pouring (while the ingot is still hot). The inner part of the flame is a reducing flame and robs the trace copper oxide of it's oxygen (removing the red hue). Sometimes the simplest answers are the best. Regards; Dr. Poe 8)
Click to expand...
Aside of the two small facts that the Rand refines gold to 9999+ and that the torch flame is used for surface finish and not for color, you'd be correct: The simplest answers are the best, sometimes.
http://www.youtube.com/watch?v=nQ37SFKahc0&feature=related
 
Another option for removing the red color is to flux it off while molten using niter. If, while looking into the molten pool of fine gold, you see a haze on the surface of the molten gold, add a pinch of borax and when it settles to the wall of the clean crucible add a pinch of niter. The niter will react with the copper and it will bounce around the surface of the melt forming an oxide which will eventually stick to the small sticky spot made by the borax and then it won't pour out with the gold.

In the older text's they refer to this process as toughening.
 
I use this same process 4Metals mentions and it works great for clairfying the last bits of contamination from gold before casting.

Be sure not to over do the niter or you may end up with your gold spitting out of the dish if it is very dirty. A little extra borax helps prevent this.

Also make sure your gold is fully molten before adding any niter.

Thanks for this tip 4Metals, I've really grown used to using it.

Steve
 
HAuCl4 said:
Dr. Poe said:
In jewelry casting, the reddish surface coat is due to traces of copper contamination. The copper oxide is polished away with fine grit on a buffing wheel. In the South African Rand, ingots of gold are polished by a large flame from a torch immediately after pouring (while the ingot is still hot). The inner part of the flame is a reducing flame and robs the trace copper oxide of it's oxygen (removing the red hue). Sometimes the simplest answers are the best. Regards; Dr. Poe 8)
Click to expand...
Aside of the two small facts that the Rand refines gold to 9999+ and that the torch flame is used for surface finish and not for color, you'd be correct: The simplest answers are the best, sometimes.
http://www.youtube.com/watch?v=nQ37SFKahc0&feature=related
Click to expand...
Actually I was referring to the almost single molecular thickness on the surface and of a copper contamination of less than one part in ten thousand. Having pure gold with minute surface discoloration is certainly not a new thing for me or any manufacturing jeweler. Yet, if it doesn't easily polish off, then it should be refined again. Regards; Dr. Poe 8)
 
hrushi said:
Dr. Poe said:
In jewelry casting, the reddish surface coat is due to traces of copper contamination. The copper oxide is polished away with fine grit on a buffing wheel. In the South African Rand, ingots of gold are polished by a large flame from a torch immediately after pouring (while the ingot is still hot). The inner part of the flame is a reducing flame and robs the trace copper oxide of it's oxygen (removing the red hue). Sometimes the simplest answers are the best. Regards; Dr. Poe 8)
Click to expand...

Which gas is used oxygen, propane, argon, or nitrogen??
can u elaborate more
hrushi
Click to expand...
I'm not sure what fuel they use, but I know that it is bottled and not smokey (most likely it's propane). The fuel is burned with oxygen. Swest. sells a flux guaranteed to eliminate red or pink gold. I think it might be a mixture of anhydrous borax and potassium bisulfate. Dr. Poe 8)
 
hrushi said:
some video i saw some white colored crucibles what are those made of
hrushi
Click to expand...
I've seen off white crucibles of either clay or zirconium oxide. The zirconium crucibles are often mixed with silicon carbide, a gray to black color. Clay crucibles are made to be used once, then thrown away. I've gotten several melts from some of them, as much a eight times. Zirconium crucibles have a relatively short 'life span' compared to the silicon carbide. The silicon carbide is my favorite. Dr. Poe 8)
 
hrushi said:
what is difference between silicon carbide and graphite
which mold or die is better considering durability
hrushi
Click to expand...
Silicon carbide for crucibles, and cast iron for molds. Watch the video of the Rand refinery a dozen times. Did you notice the wash in HCl after the ingot is cast?.
Graphite molds give very good finish, but they wear out fast. If you can make them yourself cheaply they are a good alternative.
 
How would one go about obtaining niter? I googled the term and read the wiki, i'm getting the impression it is gun powder of sorts? Is it a salt we can make by doing some chemistry with nitric or just slice open a firework?
 
Considering the purpose of the niter is to clean up some gold which is a little contaminated to begin with, I would resist using anything less than technical grade niter. (potassium nitrate)

God only knows what else is in fertilizer grade chemicals.
 
Is the addition of niter something which would be recommended for every melt or is there a more specific circumstance for its use. For example, if I am stripping finger foils with ap then copper is the main base metal of concern and something I would go to great lengths to clean off before dissolution of the foils and melting of powder. If I was silver inquarting followed by nitric then copper may not be the main concern although It may still be a mild contaminant.
 
The clean up of gold in molten form is sometimes required when trace impurities make it past your washing and cleaning processes on the powder.

In lieu of refining the brown powder a second or third time you can quickly clean the molten gold of trace impurities using molten borax and niter.

If the brown powder melts with a clean surface to begin with there is no need to use the borax/niter cleaning process on it, so don't make it a habt of always adding borax and niter to your melts, use only when needed.

The surface of molten gold should look green and clean all the way across the surface of the molten pool. If you pull your torch away for a short moment and see what looks like floating debris, colored rainbows, or swirling patterns in/on the molten gold, then proceed to use the cleaning procedure.

This process will not remove silver contamination from gold. For silver contamination you will need to refine a second time and properly rid the powder of silver in the wash/cleanup phase or in the filtration cycle using iced solutions.

Steve
 
On the 1st page of this thread HAuCl posted a formulation for flux using Manganese Dioxide. In addition to scavenging silver it will scavenge copper. If you are bent on melting the foils to scavenge copper try this flux.

Since foils are from electroplating, they are high purity with possible surface contamination from the under-plating. I would be leaching in nitric to clean it up.

Considering you plan on refining it further I would try running it in aqua regia without a leach or melt/flux. The thin foils will dissolve quickly and a small amount of base metal will not hinder you from dropping high purity gold from the solution.
 
Great information about the manganese dioxide removing silver, I was not aware of this one. I'll have to remember this when I melt and suspect silver contamination.

Thank you!

Does the silver get removed via vaporization or does it report in the slag as another silver compound?

Steve
 

Latest posts

Back
Top