Chalk Crayon Symmetry Magic

Third grade is on their art-history-quest, and we're up to Stonehenge.  With Stonehenge, I talk a lot about symmetry.  If you want my Smart Notebook file for Stonehenge, you can download it here.  We do a couple of symmetry projects, and the chalk crayon lift is the first one.  

This is a lesson shared with me in college by one of my professors. (Thanks, Dr. Smith!  I've gotten a lot of mileage out of this one!)  It works like this: students fold a 12 x 18 paper in half (I have them write their name and class code in marker and then turn it over or turn their name to the inside).  Using light and bright colors of chalk, they cover one side (9 x 12 size) with chalk:

Student working--I have them just do a design,
not spending lots of time on anything intricate.

To keep things [relatively] clean, we put our papers in folded newsprint in our folders at the end of class.  Once the whole side is covered with light and bright chalk, they completely cover what they just did with a heavy layer of black crayon:

This one is pretty much done.

A done one with a needs-a-lot-more one.

This is the point in the lesson that you'd better be sure they really like and respect you as a teacher, because the black coloring can get UGLY fast.  Be prepared for lots of whining. But have no fear!  The awesome part is coming, and you'll be their hero again before you know it!  I really keep them all together on their steps (ie, no one moves on to the last step until everyone is done with black crayon), so it's beneficial to have a little "filler" project for the early finishers.

Once everyone has their black crayon done, we turn that part to the inside, and use pencil on the outside to draw a picture (I say no words, but they always sneak some in).  

I have them use fat/kindergarten-type pencils so they get a thicker line, and they have to press pretty hard.  The pressure of the pencil lifts the crayon off the chalk, and viola!

These are really cool, and the students love the final product, but I'm struggling with wanting a specific theme for them to draw.  It seems like there's no "middle" with this project, they're either amazing or a scribbled mess.  We'll see if I think of some sort of theme for their drawing before next year.