Harris, Peter J F (1999). "On Charcoal". Interdisciplinary Science Reviews. 24 (4): 301–306. doi:10.1179/030801899678966. Diakses tanggal September 15, 2013.
Harris, Peter J F (1999). "On Charcoal". Interdisciplinary Science Reviews. 24 (4): 301–306. doi:10.1179/030801899678966. Diakses tanggal September 15, 2013.