Firstly, those are beads of jade for beauty. Secondly, christianity didn't gain a foothold in China until the seventh century, and the fireworks at the end of the movie indicate it was set during the Sui dynasty which ruled China from 589 to 618 A.D. Thirdly, if you look at the last bead at the end of the string, you'll see what looks like a drop of lube dripping from the end of it.
Its the clasp thats reflecting light