Viking age bead, barrelshaped. Ligth blue bottom with stringer decoration in blue and red. . This seems to be the most common shape but the same decoration also appear on biconical and tubical beads.
They seem to be quite common and spread over a large area.
A group of these have been found in a ninth-century grave at Reine in Buskerud. They can be seen in the top rows in one of the pictures in this great article by Text and Trowel. They are belived to be made in a workshop at Birka.