, to represent duality. Compare the Chinese characters 二 and ⺀. This glyph was conventionally colored black. The phonogrammatic value of j is derived from its use as the dual ending, -j.
Logogram for -j(dual ending), originally replacing (for superstitious reasons) the device of writing the determinative twice in certain contexts.[since the Pyramid Texts]
Written in place of two difficult-to-draw signs.[mostly since the 19th Dynasty]
Gardiner, Alan (1957) Egyptian Grammar: Being an Introduction to the Study of Hieroglyphs, third edition, Oxford: Griffith Institute, →ISBN, pages 536–537
Peust, Carsten (1999) Egyptian Phonology: An Introduction to the Phonology of a Dead Language[1], Göttingen: Peust und Gutschmidt Verlag GbR, page 48