^ 1.01.11.21.3Al-Bakhit,
M. A., Bazin, L. , Cissoko, S. M., Asimov, M. S., Gieysztor, A., "History of Humanityltural Development: From the Seventh to theth Century (Vol 4)" 43-5, Unesco (May 2000). ISBN 978-92-3-102813-7.
^Needham, Joseph (1986), "Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology; Part 1, Paper and Printing (Pt.1)" p.148, Cambridge University Press. ISBN 978-0-521-08690-5.