[Luddite]

If you're seriously considering laser etching/engraving, Mr Gazza, discuss your design with the engraver before committing yourself. Although, as you say, metal is a known quantity, how it reacts to the laser depends a lot on its thickness. For example, my stainless exhaust skins at 0.7mm were too thin to be safely etched, so they were laser engraved instead.

If you tell the engraver what metal you plan to use and then ask what the minimum thickness should be, you can then order your materials accordingly.

I'll be interested to see your artistic vision!