Christopher Masters (2003). Forma. Grove Art Online. Oxford Art Online. Oxford: Oxford University Press. Accessed January 2019. doi:10.1093/gao/9781884446054.article.T028979. (subscription required).
Christopher Masters (2003). Forma. Grove Art Online. Oxford Art Online. Oxford: Oxford University Press. Accessed January 2019. doi:10.1093/gao/9781884446054.article.T028979. (subscription required).