There are two reasons the Art Gallery of Nova Scotia does not permit photography in the gallery - protection of the artwork and protection of the copyright.
Light - both visible and UV - actively deteriorates art, with a spectrum of materials that range from very sensitive (paper, natural dyes) to not very sensitive (varnished oil paintings). Light damage is cumulative - it adds up over the course of an artwork's life and is not reversible. Within the Gallery, light levels are carefully controlled, both in terms of the amount of light and the quality of light to ensure the least amount of damage over the course of a display period. Above is a detail of a pencil and watercolour drawing by Franz Johnston (Group of Seven) which has suffered extreme fading - only its title, "Birches", directs your attention to what you now see as only a faint outline where the trees once rose out of the less-faded ground. This work came into the gallery’s collection in this condition and now resides in our Study Collection as a sad reminder of the damage light can inflict on sensitive objects
You will notice when you visit our Oyler gallery that it is dimmer than surrounding gallery spaces. That is because the Oyler gallery primarily exhibits works on paper, which are far more sensitive to light than the oil paintings in surrounding galleries. As such, the light levels are kept at a lower level (50 lux) to balance the need to both see the work and to protect it. In another gallery space, there are sensors that activate the lights only when someone enters the gallery, another method by which we can limit the light damage to sensitive artwork.
The Art Gallery of Nova Scotia also follows a policy which stipulates that for every 6 months a sensitive artwork is on exhibition, it must then spend two years in dark storage. This doesn't "heal" the damage, but it does allow us to ensure that future generations can enjoy these sensitive objects in a condition close to what the artist intended his/her work to look like. Preventive conservation is an important part of our role as steward's of Nova Scotia's art collection.
The intensity of a flash is hundreds to thousands of times stronger than the light a work is normally exposed to. Even though the flash is for a much shorter interval, if we had just one person take a flash photograph every day for six months, the cumulative light exposure would be over six times more than it would be exposed to just by exhibit lighting over those same six months. By that measurement, the work should then be kept in dark storage for 14 years!
And a flash doesn't limit itself just to the item being photographed. Every artwork in the vicinity is impacted by that light, so while you may be photographing a bronze statue, the nearby watercolour is also exposed and irreparably damaged by that intense light.
But what about photography without a flash? It poses no physical threat to artwork, but it does cause problems because of the copyright of an artwork.
There are several rights inherent in the creation of art - copyright, exhibition right, and moral rights. Physical ownership of a work of art does not give you any of these rights unless explicitly licensed or given by the artist, normally at an additional cost.
Copyright of an artwork belongs to the artist or their estate for 50 years following their death. This holds true even when the physical owner is the Art Gallery of Nova Scotia. While many artists grant the AGNS limited license to use the images of their work for exhibition and internal publication purposes - including this website - it is rare to be given the copyright ownership by a living artist.
Copyright allows an artist to have control over how their work is used and in what context. To use an image of their work requires a license and there is a fee for each use. If you're interested in looking at the regulations and the fees involved, please look at the Canadian Artists Representation Copyright Collective
In this instance, it's not the act of taking the photograph that's harmful (particularly non-flash photography), but the use to which the image is then put. Did you post that image to Twitter? Facebook? Flickr? You have then officially infringed on the artist's copyright unless you explicitly sought out the artist and gained their permission (and paid them the required fee) to use that image - and they can approve the image itself. The agreements on public sites like Twitpic, etc. normally state that you waive any right of ownership to those images, and they can then be used and dispersed, further infringing on that copyright.
Copyright fees are necessary and a prime source of income from visual artists, as well as writers, and their moral rights allows them to prevent their work from being associated with unapproved causes. The work on exhibit by the Art Gallery of Nova Scotia at any given time is a mix of art in the public domain (copyright has expired), art to which the Art Gallery of Nova Scotia owns the copyright for (ie. Maud Lewis), and art with the copyright maintained by the artist or their estate. As such, it is simpler to have the rule that no photographs are allowed unless permission has otherwise been sought and granted by the Gallery.