When doing research on a specific artist, it's a good idea to check whether there is a museum or another type of institution dedicated to the artist's work. If there is, it's worth checking out the museum's web site. Nowadays many institutions offer superb materials and links on their sites, available for free. There certainly are good, authoritative sources available for the world's most famous artists.
For example, the Van Gogh Museum in the Netherlands has established a blog. The Van Gogh’s Studio Practice provides access to collaborative research projects in art history, technology and natural science. The objective is to gain new insights into Van Gogh’s working method by investigating every facet of his creative process and his works of art, and through comparison with his contemporaries.