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

Corrosion in Metals

Metal Passivation: Preventing Iron from Getting Active

What Is Brass: Typical Grade And Applications - LEADRP - Rapid Prototyping And Manufacturing Service

Does brass rust? Why or why not? - Quora

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

The Effects of Oxidation on Copper

Self-healing metal oxides could protect against corrosion, MIT News

metal - What is this white layer on brass? - Chemistry Stack Exchange

Preventing Oxidation: The Purpose of Metal Polishing

Nickel Aluminum Bronze Corrosion Resistance - National Bronze Manufacturing

Tech Steel & Materials What Metals Don't Rust or Corrode

Does Brass Rust?

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

What Causes Brass to Tarnish and How to Restore Its Faded Beauty