My 9999 gold button seems dirty after melt

[giahylxag]

I can be sure that my button is 9999 because I used 9999 (PAMP) gold bar to make it
But on the top of the button we can see a small layer of residue. I really don't know what it is. It is not shiny, it really irritates me.
I used a new graphite crucible. Melted the gold and let it cool naturally to make a round button
I used my hand to put it in the crucible, so may it got dirty from there?

This is the second button

Took a test, still got 99.99%. Machine is Vanta GX SDD, brand is olympus

 

[anachronism]

Cameras play tricks depending on the light so I cannot comment as to whether it looks like 4 nines gold however three things if I may. Firstly boil the button in Sulphuric Acid. 20% will do. If it's flux on the surface this should get rid of it. Secondly get a carbon mold to pour your gold in and then empty the solidified gold into a jar of water (not plastic, unless its a large volume of water) this serves the purpose of shattering off most of your flux instantly. Finally if you're melting 4 nines gold you only need a really tiny amount of flux if any at all. Use less.

 

[giahylxag]

Cameras play tricks depending on the light so I cannot comment as to whether it looks like 4 nines gold however three things if I may. Firstly boil the button in Sulphuric Acid. 20% will do. If it's flux on the surface this should get rid of it. Secondly get a carbon mold to pour your gold in and then empty the solidified gold into a jar of water (not plastic, unless its a large volume of water) this serves the purpose of shattering off most of your flux instantly. Finally if you're melting 4 nines gold you only need a really tiny amount of flux if any at all. Use less.

There are 2 things I want to make clear:
1. I tested on a Xrf machine on both sides and the result showed 9999 (as expected since I used PAMP 9999 bar to make these buttons)
2. I used a fresh new crucible and didn't use any flux. I just melted it and waited for it to cool anturally

 

[Yggdrasil]

There are 2 things I want to make clear:
1. I tested on a Xrf machine on both sides and the result showed 9999 (as expected since I used PAMP 9999 bar to make these buttons)
2. I used a fresh new crucible and didn't use any flux. I just melted it and waited for it to cool anturally

As Jon say, pictures are not the best to relay your impression of the button.
It have the hallmarks of high purity.

 

[anachronism]

Whilst I'm not entirely sure why you'd melt down ingot bars to make a button (but that's your prerogative) are you sure they don't have a lacquer? I would try the Sulphuric boil and see what you get.

 

[Yggdrasil]

There are 2 things I want to make clear:
1. I tested on a Xrf machine on both sides and the result showed 9999 (as expected since I used PAMP 9999 bar to make these buttons)
2. I used a fresh new crucible and didn't use any flux. I just melted it and waited for it to cool anturally

Did you melt the bar directly?
Just from the top of my head, might there been some loose dust in the Crucible that has melted and covered the button?
I suggest you do what Jon say, boil it in dilute Sulfuric.

 

[4metals]

Another very old trick to clean up a bar is to add a pinch of borax to the molten metal. Just enough for it to migrate to the side of the crucible and stick there. Then add a prill or 2 of potassium nitrate (niter). The prill will dance around on the surface and oxidize contaminants and they will adhere to the sticky borax spot.

When melting fine gold (without flux) I like to look straight down into the pool of gold. Usually it is like a mirror and I see myself. But on occasion I see a film. That is when I use this toughening technique.