If you are trying to cite information from a museum website, such as a museum written description of an artwork, it is recommended to cite it as website with the museum as the author in addition to having a reference for the actual artwork.
For APA, I would use the following format:
Name of Museum. (date). Title of webpage. Retrieved from URL
Here is an example using Jackson Pollock's Number 5, 1950, which is owned by the Cleveland Museum of Art:
The Cleveland Museum of Art. (2016). Number 5, 1990: Description. Retrieved from http://www.clevelandart.org/art/1980.180
For MLA, I would use the following format:
Name of Museum. "Title of webpage." URL. Accessed date.
Example: The Cleveland Museum of Art. "Number 5, 1990: Description." http://www.clevelandart.org/art/1980.180. Accessed 4 December 2018.
