Musings on Photography

One More Thought on Longevity of Gelatin Silver Prints

Posted in materials by Paul Butzi on April 21, 2007

One more random thought to throw into the discussion of the (assumed) great longevity of gelatin silver prints.

One of the big issues surrounding inkjet printing has been the use of papers which have optical brightening agents (aka OBAs) in them.  There are huge, longwinded discussions about the problems with OBAs, and I’m not even going to try to recap the discussion here.  But there are apparently serious concerns about the longevity of any print made on paper that has OBAs, because the OBAs lose activity/evaporate/fade over time, and so the print ‘yellows’ as the paper base loses whiteness (and perhaps other bad things happen).

Prior to 1950, no commercially available gelatin silver paper had optical brighteners.  After 1966, most did.  My understanding is that virtually all currently available gelatin silver papers have optical brighteners.

Just something to keep in mind when you’re pondering whether the longevity of prints made 100 years ago has much to do with the longevity of prints made today.

2 Responses

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  1. Michael Gordon said, on April 23, 2007 at 9:36 am

    Paul: I’ve never seen it suggested anywhere that OBA’s do anything other than slow down the rate at which a paper would otherwise yellow. OBA’s perform the same purpose in laundry detergent. The ‘color’ of the paper is clearly affected over time, but I don’t see how OBA’s threaten the longevity of a print (silver or inkjet).

  2. Paul Butzi said, on April 23, 2007 at 10:03 am

    OBA’s don’t do anything significant to the base color of the paper, what they do is fluoresce in the presence of UV, and thus make the paper appear brighter and whiter. As you point out, they do for prints what they do for laundry, making the prints ‘whiter than white’. If the paper base is non-archival and yellows over time, I don’t know that OBAs will retard that process. Maybe they do, maybe they don’t. Offhand, I’d suspect that they don’t have much effect.

    But ‘longevity’ is defined as ‘how long the print continues to look the way it looked when it started’.

    So if the print starts out looking like it has a very bright base (because of OBAs) and the OBAs diminish in effectiveness over time (either because they vanish, or simply lose activity, whatever) then the appearance of the print will shift over time, as the base no longer has the benefit of the brighteners and takes on its ‘natural color’.

    That is, longevity is not ‘how long can we recognize the subject of this photograph’; it’s ‘how long will this print look exactly the way it looks now’.

    Bottom line: OBA activity in the paper base is not stable over time. So the appearance of any print which has OBAs in the base is not stable over time.

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