Graffiti is the only form of artistic self-expression that can get you both arrested and exhibited. Its most celebrated exponent, Banksy, is the subject of tabloid news speculation. The faces and names of most graffiti artists are even more of a closed book. Until Crack & Shine, that is. Gaining exclusive access to these creative renegades as they work, the photographer Will Robson-Scott shines a light into occluded corners of nighttime London where graffiti art finds its stealthy way onto brick walls and tube carriages.