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This is a question which is highly discussed on the Internet but I've been researching for a long time and I've never found any scientific proof backing this up.

It's known (or at least spoken of) that intense light creates an effect called "photo-degradation," which makes colors like red fade away and turns white into yellow or brown, as can be seen on many items from our daily life.

Every museum containing ancient art forbids the use of flash when taking photographs or even forbids photographs at all but some people claim this is just a rumour or an habit that has been passed down from generation to generation of museum keepers.

So is it true that flash hurts art or is it only a myth? Scientific backup is much appreciated in this discussion.

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Strangely, 'no flash photography' is a very helpful policy. Have you ever tried to shoot art somewhere where it is allowed? You can't get a good shot! Why? Because all your photos have a picture of someone else's flash reflecting on the artwork. –  Itai Sep 21 '11 at 15:33

3 Answers 3

up vote 79 down vote accepted

Yes, it is true. Xenon arc lamps (flash tubes) are a common light source used in accelerated aging tests, and will cause the breakdown of light-reactive (or "fugitive") pigments, as well as speed up the physical deterioration of paper, canvas and similar grounds. You can do a web search on the terms "accelerated aging pigment xenon" (without the quotes) to retrieve a number of scholarly papers on the subject, among them Pursuing the fugitive: direct measurement of light sensitivity with micro-fading tests (Whitmore) and Poly (vinyl acetate) paints in works of art: A photochemical approach. Part 1 (Ferreira et al).

(Most of the very recent work, admittedly, has involved pigments and binders for use in prosthetic devices -- nobody wants reverse tan lines on a very expensive artificial limb, or worse, on a facial prosthesis. The results still hold, but you'll have to page through results to find specifically art-related papers; archival testing of artists' materials is old science. See The Artist's Handbook of Materials and Techniques (Mayer, 1940; 5th edition 1991) for an extensive discussion of pigment, binder and ground lightfastness.)

No, your flash probably isn't going to do a whole lot of damage when you take a single picture. But think for a moment what you're doing when you take a flash picture: you're essentially throwing a substantial fraction of a second worth of sunlight (the quality of light -- that is, the distribution of the light's amplitude across the visible and near-visible spectrum -- is very similar) at your subject in the space of a millisecond. Now multiply that effect by hundreds or thousands of museum visitors every day for years on end. The museum might as well put the painting outside under the noonday sun.

Simply filtering out some frequencies, like UV and IR, won't help with the pigment destruction; those pigments tend to break down under the influence of visible light (it's what gives the pigments their colour and brilliance), though it does help to prevent damage to the support/ground and pigment binders (oils, resins and gums are more sensitive to UV and IR damage).

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I find your explanation on the matter quite good and will read on accelerated aging xenon for sure. Please clarify one thing though, most museums are lighted with a dim light which has a different colouring from most common light bulbs. Does exposure to this light damage art as much as flash over a day or the contrary? I heard some people saying that this light is filtered as to avoid Photo-Synthesis or at least reduce it to a minimum to slow down the destruction of the pigments. What is your opinion on that? –  Hallaghan Sep 21 '11 at 10:08
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I've been slightly involved in work at the UK National Gallery, and one of the things the Scientific department are interested in is monitoring the light levels both visible and UV in the exhibition halls in near real time. Unfortunately I wasn't involved in that particular project in any significant way so that's all I know about it –  Phil Sep 21 '11 at 10:48
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+1. The general problem you're describing in the second paragraph is often referred to as Tragedy of the Commons (en.wikipedia.org/wiki/Tragedy_of_the_commons) –  Kim Burgaard Sep 21 '11 at 13:09

The risk of photo-degradation depends on materials and dyes used. Many related studies on different materials have been gathered into book "Effects of Light on Materials in Collections: Data on Photoflash and Related Sources" by Terry Trosper Schaffer. According to studies presented in that book, there are certainly some materials which are sensitive to visible light, e.g. anthraquinone dyes or natural dyes in watercolor.

Note that determining how light-sensitive are the materials used in a piece of art might require more knowledge and tests than practically achievable in museum settings, so it's much easier to ban all flash photography instead of selective permission.

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+1 for being the first answer to actually cite a reference :) –  AJ. Sep 21 '11 at 14:51
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there is more to the story here: volume and time. Any single flash is a trivially minor insult to light sensitive materials, but consider a tourist attraction which may have 5,000 visitors a day and is open to the public the better part of the year. Some neolithic painting caves have been closed to the public because the moisture from people's breath was condensing and destroying the artwork. But the idea that a single person's breath on its own might be damaging seems ludicrous on its face. –  horatio Sep 21 '11 at 19:22

"Photo Degradation" refers mainly to the effects caused by prolonged exposure to UV light (light in the range of 10 nm to 400 nm). This is the same radiation that causes a sunburn on a hot summer day. Many pigments and organic fibers in historical artifacts and artworks are susceptible to high intensity UV. If you leave a newspaper in the window you will see it turn yellow faster than one kept in the shade. This is due to the combined action of UV exposure and the acid content of commercial newsprint. The UV radiation breaks chemical bonds in materials causing them to deteriorate.

However, most modern xenon or krypton camera flash tubes produce only a small amount of light in the harmful UV range. A study cited at the University of Cambridge claims that the existing ambient light in a typical museum gallery is roughly equivalent to 30,000 consumer-grade camera flashes per day.

In most cases camera flashes wouldn't contribute substantially to a material's degradation short term, but remember that UV exposure is cumulative. Museums wouldn't show anything at all if they merely wanted to preserve things. It's an archival compromise and in the long term lessening exposure, however little, is beneficial for future museum patrons.

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