January 17, 2005
It seems my Google skills are suffering.
In response to the recent brouhaha over some problems at MoMA, especially regarding flash photography in the works on paper galleries, I posted a bit of an incredulous reply to someone at Gallery Hopper who questioned the scientific basis of a ban on flash photography. I thought I'd champion taking a conservative tack if no compelling evidence refuted the danger. I couldn't find much by way of contrary arguments via Google, and so was pretty well content to quote MoMA itself and the Library of Congress on the matter of light damage (no direct mention of flash bulbs in either) and leave it at that.
Todd Walker did his own bit of Googling on the topic and found a page refering to an apparent debunking of this danger from August 1996 on the inestimable Conservation DistList, but offering no real details. Now, while I never thought that my searches were exhaustive or decisive, I was surprised that I hadn't gotten a hit on this. I just assumed that my various casual Googles on the topics of conservation, light damage and flash photography would pull up any existing references from the DistList (which would have been my go-to resouce on the matter). Hell, I even threw in "distlist" as a search term a few times.
In part I assumed this because it's always looked to be a pretty well-indexed resource. For one thing, when Googling my own name (you see my true colors now, folks), among the top three results was always a single question I once posed to the list. As this is no longer the case (and considering the lack of hits I was getting) I figured either they've changed their robot policies (by which I mean this, not this) or their PageRank had somehow taken a hit, apparently leaving a Googler blind to their expert opinions. It couldn't possibly be my own incompetence.
Prompted by Todd's find, however, I thought to actually try out the CDL's own search utility, simply searching for the term "flash." Lo and behold, the search quickly revealed a thread containing this thorough debunking of the flash bulb myth. It took all of three minutes. Looking back, it seems the simplest of Google searches—try "distlist flash"—leads to another copy of the same post (not to mention some other good stuff). Grrr. Suffering on account of my own desire for complexity.
The underlying principle for any such calculation is reciprocity, the notion that light effects are cumulative in a simple additive manner. Reciprocity has been found to hold with reasonable accuracy in several industrial studies of textile light-fading, in at least one copying machine flash tube study, and most recently in a paper I just accepted for the upcoming ICOM-CC conference, by Saunders and Kirby of the National Gallery London. It is far and away the best study to date, on several historically important colorants, and finds reciprocity holds very nicely. While it is true, as someone noted, that some chemically measured effects linger in the dark (e.g. free radicals have been shown to take many hours to decay in photodegradation studies of wool) there is no evidence that this is a significant correction to estimates based on simple reciprocity. (Ezrati has a paper in the upcoming ICOM-CC conference showing intermittency has no significant effect on dye fading). So, the rest is arithmetic, and units.
An electronic flash on a camera is typically sized to use f8 for a film of 100ASA at a subject distance of 3m (10ft). From photo handbook data, this is equivalent to a light dose at the artifact of about 30 lux seconds (lx-s). An alternate route to this estimate is via the Illumination Engineering Handbook data: Xenon flash tubes for photography range from 10 to 200 Joules rating. Given efficacy of about 50 lumens per joule, a wide-angle reflector throwing the light forward into about 1/4 of the sphere, this gives a range of 20 lx-s for little builtin flash to 400 lx-s for big fat studio tubes.
For convenience, round up to 50 lx-s for each amateur. Assuming the gallery lighting is the lowest most museums can tolerate, 50 lux (5 foot candles) then each flash adds the equivalent of one second of normal gallery exposure. So, 300 amateur flashes a day is equivalent to adding five minutes to the display day. In order to actually increase damage by 10% on a ten hour day, one would need to experience 3600 flashes per day. Two large professional flashes would raise the ante a little, they would need 225 flashes a day to add 10%. For museums at 150 lux (15 footcandles) these numbers become 10,000 amateurs, or 700 pros, every day. To actually double fading would need 100,000 amateurs a day. Most museums would kill for those attendance figures! As for the UV wrinkle, xenon is used because it has a spectrum very close to daylight (6,000K). Given typical glass tubes and plastic diffusers, the UV ratio will be a little higher than properly filtered light, but UV type damage is far from the Achilles heel of artifacts at controlled light levels, it is color fading, and UV is not the issue here.
In other words, flash may very well be banned for reasons of copyright, or as a disturbance to the act of contemplation (my personal vote) but there is no preservation reason. I think the ban started originally because flash bulbs (and their precursors the open magnesium flash) were a genuine fire hazard, and an explosion hazard (hot fragments) and a garbage problem. Of course, tripods, hot studio lamps, and bulky equipment are still hazards, and a photography policy still necessary, but please don't wave the red flag of conservation over flashcameras.
So I stand corrected.
Spread the word far and wide, friends. We've got a Dark Age to end.
*Update: Todd Walker
"Flash Bulbs and Artifact Preservation: Myth Debunked!"
Posted by Dan at 12:12 PM
Abbey Newsletter: The Effect of Light from Flashbulbs and Copiers
An Extended Standard for Robot Exclusion
Conservation DistList Archives
Conservation DistList: Flash Photography—Stefan Michalski
Conservation DistList: Search Page
Gallery Hopper: Comments: Hordes clear $20 barrier
Gallery Hopper: The Great 'No Flash Photography' Scam
Google Search: distlist flash
Library of Congress: Preserving Works on Paper: Manuscripts, Drawings, Prints, Posters, Maps, Documents
MoMA.org: The Collection—Conservation FAQ
Modern Art Notes: Confirmed: Truitt damaged
Modern Kicks: risky business—Comments
SNL Transcripts: Old Glory Insurance