[modelfan1]

Photo etching (better known as chemical milling) uses acid to remove
material from a piece of metal (almost any metal can be "etched") by
using a photo sensitive lacquer covered by artwork on photo sensitive
paper (called a photo mask)you want the piece to look like. The photosensitive laquer which when exposed to ultra violet light, and developed in Sodium Hydroxide, hardens and becomes impervious to the acid. The acid is sprayed on or the item can be dipped and all the metal is eaten away by the acid except what is covered by the photo
and acid resistant lacquer

Here's a diagram that may help