Nice Idea, but it does not work! Lithophane is a picture made in thin translucent material that can only be seen correctly when back lit with a light source.
Thicker area passes less light and appears darker while thinner area will pass more light and appear brighter. When done correctly, you can get a full gray scale image. It is important to start with a good image that presents both dark and light shades and a good dynamic range.
To my disappointment, the granulated nature of this particular polymer coupled with probably incorrect thickness calculations made the item non-functional and lack of any esthetic value.