Welp, this is one of those situations where I thought I was being super clever only to find out this same idea has been floating around the interwebs and Pinterest for quite some time! Oh well! I needed a paintbrush holder and I thought there was something poetic about using paint. 
I got the mason jar from JoAnn’s for $1.99 and used acrylic enamel paint. It took a good 24-48 hours for the jar to dry, which I definitely didn’t anticipate, but that’s okay!
To get the even finish, I poured a bit of paint into the bottom of the jar and just moved it around until it covered the entire glass. Then I turned the jar over on a piece of wax paper, and let the paint drip down and dry. Now I have a pretty jar for my paintbrushes!
P.S. Please don’t drink from this glass, since the paint is inside. It is strictly for decorative purposes. Thanks!