John,
Iīve been thinking the same thing about the material...the paper/cardboard doesnīt feel very permanent even if it`s easy to do all over if/when it fails.
I was thinking of some kind of plastic while working on my machine, but was too excited to get it done in a hurry...so I went the paper-way
Maybe itīs possible to cut strips from some translucent plastic lids or cans, and then try to paint them in different thickness/gradients?? I guess a guy that can handle an airbrush could do this easily, but thatīs way beyond my skills

Or perhaps take a strip of plastic and try to sand/file it down to a wedge-shape in order to get it to let more light to pass through it?? If someone is willing to try and comes up with a more permanent solution, it would be intreresting to read about it.
I agree...itīs amazing that the factory didnīt do this to begin with, but I guess they are trying to cut costs in China too these days??