This week I found a new technique using custom shapes to paint and create quick compositions on the conceptart.org forums. I decided to try my hand at it, so I went out and took some photos of the random half built and rusted out machines lying around my dad's farm. I silhouetted and combined them to make some scifi shapes to use with the custom shape tool in photoshop. By using the custom shape tool you're given more control over the size, proportions and placement of the shapes than the brush tool, it's easy to throw together some quick compositions like the one I did below in about 10 minutes.
Also by utilizing multiple layers it's easy to paint into the shapes while still maintaining their edge with the transparency lock on. I did these value sketches to experiment with the different shapes. I spent about 20-45 minutes on each one.