Does anyone happen to know the name of the technique where you put a relief on the inside surface of a translucent material, so the outside is smooth, but light shining through it has shading depending on the depth of the relief.
I'm sure I took a photo of an example of this, with a label to remind me of the name of the technique, but I can't now find it.
As @agarza suggests, your description matches that of a lithophane. According to the wiki page
A lithophane is a thin plaque of translucent material, normally porcelain, which has been moulded to varying thickness, such that when lit from behind the different thicknesses show as different shades, forming an image.
It's a curious reference suggesting the material is porcelain, which may be traditional, but 3D printing has provided an "update" to the construction. One can find lithophane creator software across many platforms and programs, allowing for different colors based on 3D printer filament selection. Image from linked site.
