This was a two day project and I've always loved it. I found out letting them draw with q-tips was a good technique to balance out the 'printed' objects.
Day One: Print a Picasso Head with found objects in black tempera paint.
Here you're seeing Day Two --Painting the head/face/hair with warm colors and the background with cool colors.
If a student was absent on the first day, they caught up by drawing their Picasso head with oil pastel...and this would be an easy alternative to stamping the objects.