Not sure if it was brass but metal was added to many clay chips for weight. Many Christy Jones chips had it, among others. Casino chips need to be about 10 grams for easy cutting.

GGS/RT Plastics makes chips any where from 8 1/2 grams to 11 1/2 grams if I remember right. Same chip they just add weight.

Thjis one has a coin inlay in it for weight.