Etching with vinegar

[Variometer]

Thanks for all the replies. I don't mind working with Sodium Persulphate myself, but when writing about things like that, I am aware that the authorities seem terrified of anything remotely dangerous with legal action always lurking in the background. Same goes for high voltages associated with mains equipment. I don't mind working with them myself, but don't want to get myself in deep water because someone has managed to damage themselves through reading whatever I write. Even the Meccano sets of old with their sharp four cornered nuts are rather "too dangerous" for the modern child. I used to stab myself with the screwdriver regularly in years gone by, but I seldom do it now because it made me more careful!
Waiting for a vinegar etch doesn't bother me too much, just dump it in and leave it overnight!
Bob