I tried this activity from Pink and Green Mama with preschoolers, and it was fun, but I think it would be a fabulous technique to try with older elementary-aged children. It is important to use blue gel glue. I tried it with both the typical white opaque and the clear gel with less than satisfactory results. They both run while they are wet and shrink so much in the drying process that the lines turn into dots.
I had the preschool kids do three squares each. On the first square I had penciled their first initials and they traced with glue. On the second square they were instructed to draw a shape with glue and to fill it in with patterns (dots, squiggles, etc).