Yoshiaki Tanizawa, Tetsuya Abe, Kaoru Yamada,
"Black tea stain formed on the surface of teacups and pots. Part 1 – Study on the chemical composition and structure",
in: Food Chemistry, 103(1), 2007, 1-7,ISSN 0308-8146, doi:10.1016/j.foodchem.2006.05.068
Spiro, M., Jaganyi, D. What causes scum on tea?. Nature 364, 581 (1993). doi:10.1038/364581a0
