Is everything a Museum owns on the walls?
No! Only about 5% of the art owned by a typical museum is on display at any given time. Although this seems frustrating there are a few reasons for this surprising stat.
Many larger museums actually see their main role as protectors and conservators of art rather than places for public education. Because of their size and funding, larger museums are able to conserve the art and house it safely while providing access to researchers who are interested in particular works.
A big portion of artwork which has found its way into the collections of larger museums is actually donated. These donations tend to happen because of tax write offs and storage costs. Whether it’s a stipulation noted when it's donated or its the policy of the museum, there may be a rule against ever selling off the works or sending them to other collections. This can mean that the archives of a museum can swell up when gallery space remains the same.
When visitors come to a museum, they are typically interested in brightly colored paintings and large sculptures but some of the works owned by museums are sketches or textiles. These pieces can be a less exciting way to use up gallery space. They are also more fragile and can’t be exposed to permanent display without expensive conservation efforts so, more often than not, they’re kept in storage.
Some museums are trying to work their archives into the visitor experience with “open storage” programs that help the public browse the art that’s not on display. The Brooklyn museum is investing in sliding racks and viewing cases and the Broad Museum in LA lets you take a look at the storage facilities from behind glass.