gouache on black card stock
Well, it's not gouache exactly. It's water based and opaque though, it's sold as a "white watercolor".
Robot was a turning point for Doctor Who, and what better to pivot on than a familiar old-school sci-fi standard, a big hulking robot.
watercolor & aluminum foil with computer CSO effect
With added silliness and very ambitious special effects, The fourth Doctor's era moves away from the "Imagination+Realism" formula which kept adults interested in the Pertwee era, to the "Big Ideas, no matter how silly it looks" formula which kept adults interested in the Baker era.
*click images to see them wallpaper sized. The first one is 1600x900, the other two are 1024x768