Our guild had a class Saturday on How to make a quilt block magnet.
The magnet was 4" square and was supplied by the teacher. It was a recycled magnet that came free on the back of phone books...remember those? The magnet was painted white for the background. We drew our block with a pencil and painted inside the lines...hard to do on a 4" size. We used acrylic paint.
We had to use a toothpick to get in tight places. I used a thin tip marker to draw the black lines after painting. I went a bit heavy on the mod podge as the last step. I wish I had painter's tape to keep the lines sharp.