I saw these laying on a bench at work and thought that they might make an interesting subject. These are the replaceable "windows" that protect our pricey laser optics from anything that might get kicked up by the laser pulse. We use "Sharpies" to dirty the windows to reduce the transmission percentage for test purposes.

They were photographed on a backlit translucent sheet. If I ever try this again, I have some ideas how to get the illumination more even.