I recently received a gold bar to re-pour into a Lithic bar. Unfortunately, when I examined the bar, I suspected it might be slightly contaminated with base metals. The bar had a barely perceptible copper huge, with a small dark patch of oxides on one end. I also noticed the bar had scratches that appeared to be made from being rubbed with sandpaper for a file. It this is done to a gold bar, you'd want to make sure the tool used was solely dedicated to be used on gold. Otherwise, it could transfer contaminates. Upon melting the bar, I saw immediate signs of contamination due to oxides forming at the surface of the gold. The only cure is to chemically refine the gold in order to remove any base metals that may have contaminated the bar. The process it obviously more demanding. However, it's the only way to achieve the clean mirror like surface Lithic Metals is known for with its gold bars.
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