i have some very similar beads- in the 1980s craftsmen/potters experimented making things by hand with porcelain clay using body colours rather than glazing, so they combined layers of colours to give this marbled effect, and made small pottery items and beads.
maybe the only reason it died out was because around then Fimo appeared- and didn't need high temperature firing.
your beads could have been made almost anywhere where there was revived interest in hand crafts at that time- UK, USA, etc.