Now then now then...
As you can see I put alligator clips on wire and run them off the battery. I put the positive on the bare steel of the blade. The little plastic lid has salt water in it, I dipped a little piece of cotton wool in the salt water and gave it a squeeze so it isn't running off onto the metal. Cotton wool goes onto the negative clip and dabs the etch.
For the etch you can just about make out some purple nail varnish(metallic!
) on the steel. I put a thin coat on bigger than the etch to avoid corroding steel that shouldn't be etched. The wet cotton wool is then gently dabbed on the etched piece until it turns nice and dark. You can hear it sizzle and it won't take long. If you kept at it you achieve a deeper etch but it really doesn't take much. I used to go to town but realised some time ago there's no need to.
You can see here it's just a very speedy process to rust the steel. The cotton wool discolours and the etch itself turns a dark rusty colour. Once I clean it off with surgical spirit or nail varnish remover it just looks dark not rusty.
The buffalo was done with a sharp needle and a steady hand but was the first try and took about 30 seconds. Basically I just got lucky. If I didn't it would be back to bare steel and another layer of dried varnish and begin again. For my maker's mark which is just initials I tend to use a blunt needle or even a ballpoint pen for fatter lettering. You don't need to scratch the steel, just the layer of varnish protecting it.
I hope this helps someone, it's easy to do and the battery and clips cost me about £5 in total. Nail varnish twocked from my wife as she didn't like that one and a bit of salt and cotton wool. Happy days eh!