A lithophane is an etched or molded artwork in very thin translucent material that can only be seen clearly when back lit with a light source.It is a design or scene in "en grisaille" (in gray) tones.
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A lithophane presents a three-dimensional image - completely different from two-dimensional engravings and daguerreotypes that are "flat". The images change characteristics depending on the light source behind them. The varying lightsource is what makes lithophanes more interesting to the viewer than two-dimensional pictures