I've seen magnets like these many places, but it never dawned on my how easy it would be to make them until I saw the plastic flat marble cabochons at TAP Plastics. I picked up 6 of the 1 1/4" cabochons.
I thought I could put the cabochon down over my yuzen paper and just cut around it with an Exacto knife and then do the same with a magnet and it'd be perfect. The ragged edges were very visible, and with the thin yuzen I couldn't squeeze all the air bubbles out of the Amazing Goop I was using. I ended up with 2 cute yellow flowers my husband or mom could love, but not so much for anyone else.
I was using a sheet of black magnet that was very thin and flexible and about 2.99 from JoAnn, perfect for cutting into size. My first additional purchase for this project was an Ek Success 1-1/4-Inch Paper Shapers Circle Nesting Punch. This cut my paper and my magnets down to the perfect size, and let me see the area I was punching.
Investment #2 was in a large size tube of E-6000. It requires the windows to be open and causes cancer in California, but the glue adheres perfect and clear without any bubbles.
With those 2 little changes these magnets came right together. Take the cabochon, put a tiny amount of the E-6000 on it, half of pea size, and then rush to get the cap back on the E-6000 before it explodes on your desk. My stock of kraft paper comes in handy to use as desk cover in times like these. Have your paper backing sitting on your desk and turn the cabochon over and push down on it until you see the glue spread to the edges and all the bubbles disappear. Clean up any glue on your cabochon now, before it dries. Let it sit for a few hours, with the windows open if in doors. Take care of any uneven paper edges with a knife, then punch out a self adhesive magnet and slap it on.
Lots of people make these with the round glass flat marbles you can get in the fake flower aisle, but they're full of bubbles and scratches, and I like having something perfectly round to use that's always the same size.