I tried this black glue stained glass for the first time this year and I love the results. The kids can do their drawing and then cover the lines with black glue. After it drys overnight they can add the areas of watercolor easily because the glue keeps the watercolor confined to each individual area.
I used an underwater dolphin scene as my inspiration. First I did a drawing with pencil on watercolor paper and then used black Elmers glue to go over my pencil lines. (I made my own black glue with black acrylic paint added to regular white glue, mixed it well and returned it to the glue bottles.) It helps to tell them to do the middle first and then work their way to the outside with the glue. I will demonstrate turning the paper in different directions to make it easier to apply the glue as well.
The watercolor washes are lessons in color mixing, wet into wet and also removing color (wipe the brush in a paper towel so it is almost dry, it will "vacuum" the paint right off the paper) in areas to create lighter areas in the wash.
It's easy for your students to create a complex looking work of art!