The first two images demonstrate exposure, or at least over exposure very well. The lighter of the images is actually overexposed, the shadows are beginning to get density and therefore the dark substrate is becoming obscured. If you are used to exposing negative film then this process is counter-intuitive, however if you think of it as transparency then it is logical. The second image has been given about a stop less light, the shadows are without density and therefore the dark substrate is visible giving more contrast overall.
Having got the exposure marked, I could concentrate more on the creative aspects of the shoot, this is the result. I am quite proud of this one.