Yes, Glass was what I expected as a solution too. In the past (20 years or so) I have used a local insulating glazing company to assemble the glass sheets I silkscreen printed for an outdoor sign. I used the different layers to create some interaction for passersby, the texts shifting to the background etc. A text/vector design on three inside surfaces including the white glass background. This insulating glass had a silica in the profile sealed in to capture any moisture. The printing had two steps, an etch on the glass first of the design to create a better bond and then alkyd based ink that hardens on oxide. It lasted longer than the lawyer firm it was created for.
You might consider that method too and have the front glass printed at the inside with UV curing inks + a white ink for reflection and add white glass at the back. It is possible with tempered glass too for better strength. In that case no extra polymers are used in the image layers that could create issues. The process could be less expensive than what you describe. Prolonged exposure of UV cured inks in sunlight is not without issues though.
Met vriendelijke groet, Ernst
December 2012, 500+ inkjet media white spectral plots.
Always good to hear your opinions and suggestions. The process I am considering using is called Dupont SentryGlas:
"...SentryGlas® Expressions™ is patent pending technology that brings together
our PVB technology with DuPont proprietary inks to create a decorative
laminated safety glass that optimizes safety, image quality, lightfastness
and glass durability. We can take an image, print it on PVB and ship to a qualified SGX glass
laminator. We are able to print up to 94" x 192"...."
As you see from the quote above, they have a proprietary printing process, using their proprietary inks, and the laminated end result adheres to their testing requirements, which they guarantee.
Since this is such a huge project, I would hand over the image to the company, and the mounting to architects, engineers and designers, so that they would be in charge of the installation with qualified installers. Since the panels would be hung on an armature, presumably, the glass would be impervious to rain from any holes, etc, for mounting.
I like your idea about the back panel being frosted or white. One thing that occurs to me, is that while being back-lit the image would be well seen at night, perhaps not so much during the day. A white panel from behind, might solve the problem, giving me the best of both worlds.
Thanks again for your thoughts and suggestions, Ernst - always a pleasure hearing from you.