One of the fun things about designing 4 layer art boards is the extra dimension you get with the internal layers. With a bit of planning, you can really take advantage of the internal layers for some interesting effects.
One of the nicer things is with a white substrate (specifically, FR408 through OSH Park), is that it’s translucent enough that you can easily see through it, but it scatters effectively enough that the design on the reverse side is heavily obscured. With a bit of planning, you can get very excellent backlit designs.
The design of this particular project was driven by my friend Jason, who wanted something neat for the SOAK festival. I simply hopped in to help with the execution, since I have a bit more experience designing and viewing boards.