Environment Sketches - Adding Value and Lighting Quickly

I Added some value and basic lighting to some environment sketches out of my sketchbook to get a better sense of atmosphere. I therefore scanned in the sketches and opened them in Photoshop. I now added a layer and set the layer mode to "Overlay". After colouring over the basic value/lighting of the image I would again create a new layer and add the picture frame. Then the sketch name on a separate layer again. This was the repetitive process for each of the images below.

Sketches