I’m obsessed with marble magnets and thumbtacks. The first place I saw these was on the Martha Stewart website.
Here are some of the magnets I’ve made
I won’t do a tutorial because there are so many good ones already out there. These are pretty popular in the crafty world. I find the flattened marbles at Hobby Lobby or Dollar Tree, and I use mod podge and super glue on mine. I also paint on a layer of mod podge on the back before gluing on the magnet. If you don’t do this, the glue can soak through the paper and the dark magnet will show through. Here is Martha’s tutorial and a few others