Bida is the brass town of the Nupe kingdom. Whole quarters of the city belong to the tswata muku, a hereditary guild of brasssmiths who work beside the Masaga glass-bead makers under the patronage of the Etsu Nupe court.

Their signature object is the hammered tray. The smith punches the entire background into a matte stippled field and leaves the leafy scrolls and the central rosette standing bright and untouched. Ornament is plain, ground is textured — the reverse of what most decoration does. The Ulster Museum holds a Bida plate raised from a spent artillery shell.