I have just designed a microprocessor controlled Electro etcher.
Thanks to Tinbasher - Zac Cheong and Stewart Townsend for the input on the reason for AC and DC current.
The design I made would do both AC and DC etch, with fully controlled etch time, steady and/or pulsed DC output, and fully controlled AC application for "coloring".
The time of current application can be individually controlled from 0.5 second to 30 seconds in increment of 0.5 seconds.
Power input is from a simple AC power supply or a transformer.
Fully tested using salt water for electrolyte and silk screen for stencil. <-- Btw, Anyone need stencil? I am arranging for pre sensitized silk screen buy, they are ready to be "Exposed" with your design and will be available in blanks of A4 size.
Why salt water? well, it is NaCl + Fe + H2O -> NaOH + FeCl3
Anyhow, here is the schematic
here is the circuit board
Finished test board and etched knife picture below.