http://www.vangoghmuseum.nl/en/125-questions/questions-and-answers/question-54-of-125

http://vangoghletters.org/vg/context_1.html

http://www.arthistoryarchive.com/arthistory/expressionism/Vincent-Van-Gogh.html

The Huffington Post is a liberal-oriented American online news aggregator and blog...so there is bias....use with caution and try to verify the facts from the fiction!
http://www.huffingtonpost.com/2015/07/29/vincent-van-gogh-trivia_n_6181630.html