Gold colored film on top of solution after stannous test

[ragood]

I dissolved some gold filled scrap foils in HCl and 30% H2O2 and put a drop in a white spoon to do a stannous test. The stannous test turned black, but then a gold colored film formed on the surface of the drop of solution. See attached picture. Does anyone know what caused that gold colored film? Thank you.

 

[Shark]

A very positive test result.

 

[anachronism]

The thing that caused that gold coloured film is ... gold. That's a good strong result there Ragood. You've done well.

 

[ragood]

I've done stannous tests in a spoon before and never saw the gold colored film before. When I filtered the solution I saw some gold colored film on the inside of my vacuum flask, too.

 

[4metals]

@ragood Your test on a white spoon is similar to testing on a porcelain spot plate. I often tell people to use a piece of filter paper or paper towel to test a drop of solution. I would love to see how your heavily gold laden sample looks on paper so we would have a comparison. A photo would be helpful if you could test it on paper.

 

[anachronism]

I've done stannous tests in a spoon before and never saw the gold colored film before. When I filtered the solution I saw some gold colored film on the inside of my vacuum flask, too.

You've probably never had such a concentrated solution before. It's all good.

 

[ragood]

@ragood Your test on a white spoon is similar to testing on a porcelain spot plate. I often tell people to use a piece of filter paper or paper towel to test a drop of solution. I would love to see how your heavily gold laden sample looks on paper so we would have a comparison. A photo would be helpful if you could test it on paper.

I have already precipitated the gold with SMB. It wasn't a very concentrated solution. I yielded only 7.3 grams of gold from about 1200 ml of solution. Since I was refining gold filled scrap foils, I had a bunch junk down in the bottom of the beaker. I used acid/peroxide to dissolve the base metal substrates leaving the foils. It took about 6 weeks in acid peroxide with a bubbler and there were a few pieces that still had base metals remaining. The scrap was watch cases and watch band caps, some jewelry and a gold filled Cross pen. Some of the foils were tiny bits so I put everything in the HCl and 30%H2O2 solution.