I use http://3dp.rocks/lithophane/ to generate the lithophanes, 120mm square, 3mm thick. I print them flat, at 0.05mm Layer Thickness. Please use a high temperature material no matter what Lighting you intend to use. I used ABS/PC to print mine. Glue may be required to get your panels to stay in place. Setting a 3mm border can eliminate the need for glue on all but the optional LED lithophane panel, which will still require glue to stay in place (0.15mm clearance on all panel edges), but will still also benefit from a border.