Dual-shot adds a second layer of colored, transparent or translucent polycarbonate on top of a base layer to produce secondary color blends and depth effects.
This negative is illuminated from the front by an arc lamp, and the light from this lamp passes through the transparent regions of the liquid-crystal layer to the middle layer.
And much to my delight, I discovered that I was able to see the city's past as well as its present: the London of my imagination superimposed upon the reality, a transparent city in which the old was encased in the new like an ancient layer cake wrapped in glistening sandwich-wrap.