Etching Brass: Should I Use Iron III or Copper II?

[Terocamo]

I understand that brass is an alloy of copper and zinc.
If I want to eitch brass under standard condition, should I use iron III ions directly or use copper II first than us Fe III ion?
I ask this because from the electric potential data, Fe metal will form under the presence of zinc if Fe III ion is directly used

 

[lightarrow]

If Fe⁺⁺⁺ is in excess, Fe shouldn't form, the end product being Fe⁺⁺ only.