Design your image. Once your done, flip the image horizontally, and invert it, so black becomes white and vice versa. Test print it on cheap paper, to make sure everything is where it should be.
Print the images to glossy paper, with the toner set to maximum. Cut them out, and tape them to your enclosure(s).
Iron the image (face down) under a cloth, for a good 10-15 minutes. This will make the toner stick to the aluminium. Allow it to cool.
Dunk the enclosure into clean water for a while, then peel the paper off. The toner should stay on the box.
Tidy up any flaws in the toner with nail varnish.
Also paint the interior with nail varnish.
Add a couple of small bits of wood to the face of your box, so there is room for the acid to get underneath. Put these in an area that won't get etched.
Dunk your boxes into the ferric chloride solution. (follow the instructions on the packet. Don't take shortcuts, or you'll hurt yourself). Keep agitating the tub, and rinse the boxes periodically.
Use fine sandpaper to remove the toner, being careful not to damage the etch.
Once you've cleaned up the box, check everything fits before painting.
Paint your etch with model paint. It's best to keep the colour scheme pretty basic.
Line the internals with foam, so you don't get any short circuits.
Give your enclosure a few coats of clear varnish, then assemble the electronics.
Stick your new, one-of-a-kind pedal onto your pedalboard, and smile as guitarists drool over it!