You can use index matching fluid to determine what the nylon line is currently at and then use the fluid to experiment with epoxy droplets containing various amounts of low index additives like MgF2 nanoparticles or something :)
Add a polarization filter coating to the epoxy? https://en.wikipedia.org/wiki/Optical_filter#Polarizer
Also, if the plastic can be "invisible", you can also house it in invisible plastic- thus creating, a exploded working model, inside the resin
Edit: A quick search reveals that there is quite a lot of prior art from the optical community. Darn, maybe I'm not done here.