This was today at our beach. I did a sketch yesterday but was not satisfied with the way it came out. I think this one is a lot better. I've added a couple of photos of the progress and the final sketch.  

Nautilus

This is a nautilus shell on our balcony. I looked left and happened to liked the way the light was striking it (with afternoon sun from behind). Tried capture the transparency of the light though the shell. I'll try again next time