Working with some plastic bead makers in Bali a few years back I was told that the pearlescent effect was something as simple as a powder (like baby powder?) added to the beads.

Language was a problem with our dialog so it may be that they really use "pearl powder" recovered from drilling pearls. I know we saw that drilling residue saved in Zhuji, the FWP center in China, where, we were told it was sold into Japan as facial powder.

When Dee experimented with various methods of heating various fake amber beads she created some sparkly crazing inside some of the beads. The pearly look is more of a surface effect.