>Since I've never seen one of Tansey's works I assume they are air
>brushed off photographic collage projected onto large canvas.
Not so modern as that. He's a postmodern painter using a premodern technique:
http://www.thefreelibrary.com/Mark+Tansey,+A+Brief+History-a01073741903
Tansey lays down a layer of monochrome pigment on canvas that can be altered easily only before it dries. This leaves him only about a six hour window in which to complete his alterations. As such, he works in a style similar to fresco painters, painting in segments that he can finish in this short time frame. Tansey creates his images by pulling away and wiping pigment, so that various textures and tones are produced on the canvas. He adds pigment to darken certain areas; and when he wipes away pigment, the white of the canvas shows through the thin layer of paint to lighten the area. This process is, by nature, largely subtractive.