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

Machined Products: Corrosion Tests Prove Free-Cutting Brass Outlasts Plated Steel

What is the difference between corrosion and tarnishing of metals? - Quora

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

About Brass Oxidation

Metals That Oxidize. Corrosion of Metals - Engineering Web

Corrosion of brass

Preventing and Treating the Dezincification of Brass – Canadian Conservation Institute (CCI) Notes 9/13

Corrosion vs Oxidation vs Rust

Nickel Aluminum Bronze Corrosion Resistance - National Bronze Manufacturing

High‐Temperature Oxidation of Metals

Corrosion