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.