Well the logo's arrived. While I was waiting I bought some electrical bits and made my machine. I went for 9v/18v with a high/low button and an ac/dc button. I made my hand tool from a chunk of brass. I'm using salt solution for electrolyte and craft felt on the hand tool. It seems to work well, I'm etching on 18v/dc and darkening on 9v/ac.
Here's the result. Thanks all for your input on this.