Preparing the Bath

I do use a Sharpie sometimes for a small touch-up but, Sharpie
ink is not as acid resistant as paint. Etching aluminum is a bit more aggressive than copper
and usually the Sharpie ink is eaten away in the process.
You've come this far... don't take the easy way out... Use Paint!!
This is all the etchant you'll need to do one standard etch.
A reverse etch may require and etchant change. I don't dilute it, I take my etchant straight up!