For me, the most beautiful backglasses are those whose global design is not only superb, but whose creators have also been inventive and creative. Graphic design is of course important, but it is not enough to make exceptional backglasses.
These are of course double backglasses, those that include mirror-like coatings and that use optical effects, such as infinite reflections.
They are not very widespread and it is normal, because they were the most expensive to produce. To such an extent, moreover, that some were produced only for the American market, the "export" versions having to be content with a simplified model.
For the first three:
➤ MARS - God Of War (Gottlieb)
➤ BLACK HOLE - US version (Gottlieb)
➤ XENON (Bally)
Mars (resized).pngBlack hole (resized).pngXenon (resized).png
And if you only have to pick five, I'll take for the last two:
➤ PAPILLON (Jeutel)
➤ PARAGON (Bally)
Papillon (resized).pngParagon (resized).png
I must admit that it's because I like the heroic fantasy and drawings in the style of Boris Valero - Julie Bell, that I preferred the latter. Because otherwise, I think that FARFALLA (Zaccaria) would have had the fifth place.