Suspecting nail polish might come in green, in blue, and in purple, I googled "nail polish as solder mask". I found one bloke who claimed to have used
enamel nail polish as a homebrew PCB solder mask. He said to use enamel, but not acrylic.
I had nail polish leftover from another project. So I looked and found neither word printed on the bottle. I tried it anyway. I coated it on the edge of an old PCB. When it was dry, I verified the polish is an electrical insulator.
I repeated the experiment with a new green bottle of nail polish with "enamel" on the label. It looked great the next morning. I verified with my multimeter that it is also an insulator.
However, I was able to scratch away both types of nail polish with my fingernail, so that would not make a good soldermask. I will try overlaying the nail polish with clear coats -- clear nail polish, lacquer, polyurethane ? -- and see if anything works. If I can get something to work, I'll report my combination. Now that cold weather has arrived in the lower 48, I am going to try to avoid any liquid that is sprayed.
I also ran across a dry film solder mask vendor
http://www.soldermask.com/dfsm.htmlbut haven't yet explored how this works.