I think challenges should test an artist's creativity as much as their modelling/rendering skills. If you choose limited themes such as Glass, you'll end up with dozens of rendered wine glasses in a month. We all know that artists with caustics have an unfair advantage when it comes to rendering glass. So in the end it becomes a challenge between Applications rather than artists. However, I think themes like Cake1's idea for "Dirt" or last month's "Artist's Workspace" and "Award" work well. just a thought, Stranger Aeons