Step 8: Paint on rivets
I also didn't have a round sponge tip paintbrush, so I wrapped a napkin around the wide end of a chopstick, secured it with tape, and used that to paint the circles.
The circles might've been a bit big for rivets, but it's a kid's play structure. My friend said they look like polka dots, but I like them.
Dip the brush in the silver paint, wipe off excess, and press onto the cardboard near a seam. Rotate the brush a little to make sure any dents in the circle brush get filled in. Spinning the brush a little will ensure a good circle. Repeat wherever you think a rivet should be.
After this, I decided the rivets should have some shadows. I had a lot of painted rivets, so I didn't want to do anything too complicated. Yes, I was sloppy and quick, and I'm okay with that.
Mix some slightly watery black or dark gray acrylic paint. Using a small paintbrush, quickly paint a C shape along the edge of the rivets, overlapping the C onto the rivet a bit. In my structure, I painted all the C shapes at the lower left side of the rivets.
While I had the paintbrush and watery dark paint, I also painted a line along the lower left edges of the reinforcing strips to make it more shadowy. That made the shadows more consistent with those on the rivets.
If you look at the dome from the top, there's no real direction that the light should appear to come from, since I painted ALL the rivet shadows on the lower left side. That's okay with me. People are likely to only look at one side of the dome at a time, anyway... and those who gaze down at the top and criticize the shadow placement can make their own damn dome.