They link their owner with the daily travel of the sun disc1. Faience examples are mostly of the Late Period, as presumably the gold masterpierce below
Blue/green glaze, L 4.9, H 1.3 W 1.0 Late Period © 2014 Musée du Louvre/Christian Décamps #AF 2288
Gold L 2.7, 1.9, W 0.8 Undated © 2002 Musée du Louvre/Christian Décamps #E 3883
Blue/grey glaze L 2.4, H 1.7 Undated © 2012 Musée du Louvre/Christian Décamps #AF 2078
Blue glaze L 2.0, H 1.5 Undated © 2012 Musée du Louvre/ Christian Décamps #AF 2082
References
1Andrews C. Amulets of Ancient Egypt, 1994, p. 90