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PlaidBastard t1_izxqpgo wrote

More likely, it was finished (ground, sanded, polished) differently either on purpose or as a side effect of manufacture (some bullion is just left how it cools in the mold, other bars are hit with torches to melt the surface and get it to re-puddle glassy smooth on the side that was down in the original casting, etc. etc).

That said, sure, different non-gold alloying metals (silver vs copper vs rhodium etc.) can affect how readily a lower-karat gold polishes, I guess, but you're probably seeing a variety of finishes/surface textures independent of the gold content, from what little you gave us to go on?

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SilenceFailed t1_j01ufw7 wrote

This is the same with soldering on circuit boards. The gloss, like in blacksmithing, occurs when all of the slag (impurities) are removed. Hitting metal with a torch is a good way to hand out impure metals.

However, you are right. Having polished stainless steel molds for glassware, it is essentially a corrosive substance like kerosene (when working with substances that stick to each other, like glass in metal), a polishing lacquer (like rouge, French word, it was green stick, not positive on its makeup), and a polishing paste, to make a seal on the metal (ours was pink, not sure if it's makeup either). To hit the full shine, we cleaned it out with alcohol when we were done. Sand paper of varying levels of grit is used to smooth it out. Now, if you want the full process, let me know. I'll post the whole thing. I used to work in a glass factory producing various glass pieces from various companies. From pier 1 to Christmas Shop to dollar stores to Walmart.

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