I think they are the sheets of copper that has been made from copper scrap.
They dip a thin sheet of copper into a electroplating bath & electoplate the copper onto it, it gets thicker with a bright clean bare copper metal crystal surface structure.
If you want to see this effect found a really easy way. So obvious & complety free.
Glass jar, small bunch inch long thin copper wire, a teaspoon of Copper sulphate & a solar panel off one of those solar garden lights. Some water. Something you want to electroplate onto, I used a old worn silver plated spoon.
As the bubbles come off the electroplation, they rise & the crystals form vertical lines.
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I don't know this for sure. but
When they do that sheet electroplating, thats when they get the rest of gold out of the copper.
What they start off with is recycled domestic copper, pipe & such.
That domestic copper, its come strait from the copper mine & been melted & made into stuff. Its been used & recycled once or twice.
They probably got most of the gold out of it in the first refining at the smelter, but not all of it. Same with some other metals like arsnic.
For the smelter to get this last bit of gold, they'd have to refine it twice, doubling their costs.
But, now they have high purity copper & its suitable of making copper electrical wire, making it worth more.... win win
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