I get the mylar with one side having a mat finish - which renders it’s l00kking like frosted glass -
The colors don’t absorb as they do with pastel paper - they stay true & bright
I’ll have to try the back-lighting! Intriguing...
http://adsabs.harvard.edu/full/1990PASP..102.1086T
Mylar has nearly the same optical properties as glass, so the back-lighting of the painting should give it a warm glow and perhaps a possible 3D depth perception, depending on the optical transmission of the paints used....................