I guess I can now say that bottle cap artwork is an annual project! Last year was the first time we attempted this project with my 4th-6th grade students and they enjoyed it so much that we just kept saving caps and did it again. Just like last year we used cardboard for the backing and hot glue to attach the caps. The only expense for this project was a bit of tempera paint and sticks for the glue guns! A few of the panels were donated to the PTO auction and the rest are now displayed on top of the book cases in the library.
After a presentation where we view lots of examples of bottle cap artwork (you can see most of the images on my Pinterest board) and discuss why artists would want to use bottle caps or other "trash" in their artwork, the students put themselves in small groups and take on jobs that need to be done. Of course I make suggestions when students are unsure, or occasionally make a poor choice, but I pretty much try to let them direct their projects. My "rules" were not to go right to copyrighted/trademarked symbols and to avoid just spelling out letters. I also suggest the students look at what color caps are available to help them get their ideas.
I did let some students break the rules with SpongeBob, only because I was impressed that they used a pill bottle as a nose. He was a lot less lumpy before the 4th graders finished gluing. :) The hardest part is for students to put caps back down exactly where they were before they applied glue.
We started off trying to paint the background of every board, but by the time some of the projects were laid out, we decided to glue them directly to unpainted cardboard. The painted backgrounds look nicer but we wouldn't have finished much if we didn't alter the plans.
One group of students was set on making a mustache. We were out of black caps so they tried blue. It looked more like a seahorse so we changed it into one in the next class.
I was so sick of peace signs! I think that 4 or 5 different classes tried to fix it, changing the colors, changing the shape, etc. and I was about to suggest they just move on to another idea since it obviously wasn't working when finally one group made a design and stuck with it.
...and when you don't have enough of the colors you need to make a recognizable picture, you just make a nonobjective design!
Next year I'd like to try to get a piece of plywood donated and make a more permanent mural to be displayed somewhere in the school. For that, I'll probably let students submit design ideas to make it more organized.