Why does one side of my gold bar come out like this?

[Prime estate jewelry]

Hello,

I melt my gold in house. When I make a bar, why does one side of the gold comes out smooth and the other side looks very crusty. Please take a look at the pictures. When I give this to the refinery, they drill both sides. The one with the crusty side shows a lower karat reading. I have a Thermofisher gun as well. Looking forward to the responses.

Thank you

 

[Yggdrasil]

Hello,

I melt my gold in house. When I make a bar, why does one side of the gold comes out smooth and the other side looks very crusty. Please take a look at the pictures. When I give this to the refinery, they drill both sides. The one with the crusty side shows a lower karat reading. I have a Thermofisher gun as well. Looking forward to the responses.

Thank you

Welcome to us.
Here are some questions for you.
If there is a purity difference between the sides it is probably not fully melted and homogenized.

What is the origin of the Gold?
How do you melt it?
Flux or no flux?
What kind of mold do you use?
How do you prepare your mold?

 

[FrugalRefiner]

Based on your username, and that you don't mention having refined the gold, I would say those are base metal oxides that formed when you melted the gold. Copper, zinc, and other base metals will oxidize during the melt. I would say that's what forms the junk. It's why we refine gold before reusing it.

Dave

 

[Prime estate jewelry]

Welcome to us.
Here are some questions for you.
If there is a purity difference between the sides it is probably not fully melted and homogenized.

What is the origin of the Gold?
How do you melt it?
Flux or no flux?
What kind of mold do you use?
How do you prepare your mold?

It’s scrap jewelry. I have a melting furnace. I try to pour at 2200f. I add some borox once the gold is melt and let it cook for like 3-4 mins before pouring. I am getting the same result with flux as well. I have an ignot mold.
I fire the mold before pouring into it.

 

[Yggdrasil]

It’s scrap jewelry. I have a melting furnace. I try to pour at 2200f. I add some borox once the gold is melt and let it cook for like 3-4 mins before pouring. I am getting the same result with flux as well. I have an ignot mold.
I fire the mold before pouring into it.

If there is a difference between the top and bottom side of the bar the molten metal is not properly mixed.
It also seems there are something picked up from the mold.
The discolored side is the top or bottom?

 

[snoman701]

The crust is the zinc and copper in the melt oxidizing, it doesn't take much.

Low melting point elements in alloys will tend to not be as homogenous...and they never settle on the higher karat reading on the bottom of the bar. This is why pin sampling is beneficial, as it's easier to have a uniform distribution, especially if you are using an induction melter that mixes the melt.

 

[4metals]

Is your melt furnace one of those table top furnaces with an electrical resistance heat coil? Those furnaces don't get hot enough to get a good homogeneous sample. Do you stir the melt well before pouring with a graphite rod?

Most refiners today do not accept bars that they have not melted in house and sampled themselves. Drilling a bar is not the preferred way to sample. And your flux will better serve you if it is in the crucible for the entire melt.

 

[Anil]

Segregation of lighter metallic impurities in unrefined gold happens on the top surface and not the bottom surface. when melting is done in an ordinary furnace. For large size melts, induction melting is better where the stirring effect gives a homogenous melt. A pin tube sample without piping is best for fire assay. If drilled samples are insisted upon, three or four drills on each face (top and bottom) in the diagonally opposite direction at sufficient depth should be taken.