http://onlinelibrary.wiley.com/doi/10.1525/aa.1998.100.4.951/epdf

https://www.museodelprado.es/goya-en-el-prado/obras/ficha/goya/el-quitasol/

Serra, Velázquez, and the Arno.

http://web.a.ebscohost.com/ehost/detail/detail?vid=4&sid=1b9a37e4-5488-4f0e-975b-98a42a52f4d4%40sessionmgr4001&hid=4101&bdata=JmxvZ2luLmFzcCZzaXRlPWVob3N0LWxpdmUmc2NvcGU9c2l0ZQ%3d%3d#AN=108629542&db=aph