Rubber Cement as a Mask

I was figuring out how I would mask out areas on a canvas for a group project that I am working on with some children. I remembered how easy and fun it is to work with rubber cement, and that I even had some on my messy shelf of art supples. I brushed the image of a palm tree with the rubber cement onto the canvas. When it was dry, I painted over my tree with some light green acrylic paint. When the paint was dry, I rubbed away the rubber cement and my tree appeared. Since you don't have a lot of control with the rubber cement it is easier to be carefree with the process.