Found this little gem on Reddit!
https://www.reddit.com/r/3Dprinting/comments/474tjo/playing_with_lithophanes/
http://www.youtube.com/watch?v=-SmfbEtLHMY
I never thought of printing the lithophane on its side. Cool.
Printing on its side limits your minimum thickness to twice your nozzle width in some slicers (Cura) and makes it a lot easier to snap along layer boundaries.
@Tim_Visible - very true, but with some support geometries on either side you can prevent wobble and unstick on tall panes.
And PLA has very little issues with horizontal cracking - I only use PLA for lithos.
The advantage of vertical printing is that you can get finer detail than planar printing. At least on deltas.
Maybe your lithos are thicker. I’ve only printed a couple, but I found a 1-2mm thick edge-printed PLA litho fractured pretty easily along the grain. I don’t have a lot of layer adhesion problems on other prints, though.