I recently cut my first lithophane as a birthday present for my sister. Using Vectric Photovcarve and 1/4" Corian, I created a 5x7" illuminated grayscale framed and backlit present. I found an inexpensive picture frame and was able to fit the Corian inside after machining the edges down to 1/10".
Without backlighting, it looks a tad creepy.
Turn the power on, though, and you get a nice grayscale illuminated photo. It turned out well and she was very happy with it.
I’m going to stock up on those frames and use them for future projects.
Cut in 3 passes: create .1" pocket, rough cut with .125" ball nose, and final cut with 3/64" ball nose (final cut took about 4 hours).