Search digital print with poor UV protection

I want to fade some large prints just with keeping the print under bright italian summer sunlight.

Which (digital) printing process, paper,.. would you normally not recommend if it`s about saving the print of desaturation, paling, fading?
What would you think how long it takes for a noticeable change?

In best case, the print should be stable after keeping it out of sunlight. (But that could be done with UV protecting glas and just hanging the print indoor I think)

I`ve noticed, that just advertisement posters for outdoor use have a quite poor color and brightness fastness.

As a general rule, all colors bleach in the sunlight. Lightfast colors tend to take longer to do so. Lightfast colors tend to be in the domain of artists pigments - I do not know how photopigments compare but I would not be too optimistic. Glass, even non-UV glass can be pretty good at absorbing UV and will increase the times a lot. It cannot be eliminated, though. However, one problem you will run into is that different colors fade at different rates and so the content of your image may change. Cheers, DJ