system
Given the following post, respond as if you're commenting on Reddit:
human
Why does physical gold sometimes appear dull? Is gold's lustre affected by its purity?

Why does physical gold (e.g. jewellery, gold bars) sometimes appear dull?

 Is gold's lustre affected by its purity?
gpt
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?