I did a trial run of silver etching with ferric nitrate today to test my resists, and while showing my friend the results she asked a question I wasn’t able to answer. I wonder if someone here knows the chemistry/physics behind this.
I know some etching processes are more likely than others to produce undercutting, but how and why is that possible? If the walls of the etched cavity are exposed to the etchant just as the open places not covered by resist are, why doesn’t the etchant eat sideways under the resist on the surface too?
Also, under the “pics or it didn’t happen” doctrine, here are my test pieces. The one with the cursive writing has me most intrigued- I coated it with nail polish, then scratched through it with a scribe. It’s amazing how fine and crisp the lines are! I’m imagining quite a few ways to use that technique. The one at the far right was the sole failure- acrylic paint just was no match for the ferric nitrate.