metal - Brass - is this corrosion or oxidation and why did it

I have bought a new brass Y-split water valve which is plain brass but inside is a more polished one, it was packed nicely and I opened it 2 days ago, washed it off with water for some reason, then

Why Do Brass, Bronze and Copper Turn Green? – Make It From Metal

Rust, oxidation, acid bleed

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Brass Anodizing CNC Machining Guide: Can Brass Be Anodized?

I have seen some brass oxidize to green but I have also seen brass oxidize to brown. What is causing the difference? How much copper is in some brass? - Quora

Is this corrosion? Anything to worry about? How to fix? : r/ammo

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metal - Brass - is this corrosion or oxidation and why did it happen? - Chemistry Stack Exchange

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