First. This is not a one day project. It's not a one week project. It turned into a one month project (plus another month to blog about it).
I first saw this entry on Crafty Crow. And traced it back to the original inspiration. Kind of sketchy details, but enough to go on. And here's a sketchy recap of what we did.
What we did was this...
1. We used Elmer's Gel school glue and white t-shirts from the fabric paint section of Joann's.
We found that the gel glue is hard to squeeze, so the girls used paintbrushes to apply it. It was still kind of challenging to do it gracefully.
We let it dry for a week or more. Wanted to give it time to cure and then we got doing other things. :)
2. The painting. We used acrylic paints from the craft store (you know the ones. There's a rainbow of colors, smallish bottles, about $1/pop). Squirted some paint into a ketchup/mustard squirt bottle (in the cheapola section of the big craft store. You could use a spritz bottle for a similar but different look.) and squirted paints onto the shirts. We did this on the front yard. It would be helpful to have someplace outside to let them drip dry (e.g. a clothesline or a dedicated drying rack). We let them set for another week or so. The colors co-mingled with the help of gravity as it was drying, so bear this in mind when you are picking colors.
3. Then we soaked the shirts in a bucket to dissolve the glue. I do not recommend using the sink. The drain may not be quite the same again until someone snakes it out after that experience. Wash separately from your other stuff. And there you go.