I'm trying to figure out what the most polarizable solid that can be used at standard conditions is.
Wikipedia says alkanes are the most polarizable materials: https://en.wikipedia.org/wiki/Polarizability
I also found this table of the polarizability of elements: http://ctcp.massey.ac.nz/2018Tablepol.pdf
From 1) I'd hypothesize parafin wax?
From 2) I'd hypothesize an aqueous gel (OK, technically not a solid, but still useful) spiked with an iodine salt?