Black And White Digital Printing Part 5c

The Great Paper Chase - OBAs and Alpha-Cellulose

Part of a Series on Fine Art Black and White Digital Printing
Revised April 2, 2008

Copyright © 2004-2008 Clayton Jones
All Rights Reserved

by Clayton Jones

About Optical Brightening Agents

The presence of OBAs in papers and coatings is a subject about which we seem to know very little. Some photographers seem to be more concerned about it than others. The general consensus is that OBAs will "burn off" over time and the paper will lose either some brightness or whiteness or both.

I'm not sure exactly what the relationship is between those two attributes and OBAs. Just from observation it seems like they are separate and independent. For example, Premier Art Hot Press has no OBAs and W6 color, but is brighter than some cooler papers with OBAs. Condor BW is both very white and very bright. When the burn-off happens how much of each will be lost? Will it still be whiter than Hot Press at W6? Peregrine Smooth has OBAs but is starting out already medium warm at W4. Where will it be after burn-off? Will OBA burn-off affect ink color?

Here are two on-line sites that shed some light on the subject (pun intended):

http://composite.about.com/library/glossary/b/bldef-b790.htm

http://www.solutionsforpaper.com/sfp/global/service/faq/fwa/

From these I gather that there are different kinds of OBAs, and I have been told that new ones are better than old ones. Can we therefore assume that the affect on brightness vs whiteness may differ among papers, depending on what was used, how much, and whether it is in the coating or the paper? And if so, how do we get this information?

In my discussions with various sources so far, there doesn't seem to be any certainty about what length of time is required for the burn-off to occur. It is not clear to me whether we are talking about months or years. I have silver prints on OBA-containing paper from 20 years ago that still are very bright and very white.

I had an interesting phone conversation with Diana York of Hawk Mountain Papers which addressed some of my questions about OBAs, and I asked her if she would send a summary of her remarks for this article:

OBAs are Optical Brightening Agents - chemical agents which are used to
brighten, or whiten paper and/or coatings. OBAs are also present in textiles
which are often used to produce cotton pulp for paper (cotton rag). We do
not add OBAs to our base sheets, but some residual OBAs may be present from
the textile cuttings.

We do add OBAs to some of our coatings. OBAs will break down over time and
exposure to UV light and lose some of their brightness value. OBAs will
react with dye molecules and break them apart ( I have a scientific paper
somewhere detailing this), but I have not found any scientific reports
showing OBA's reacting with pigments.

But OBAs are not the only things that make paper and coatings "white". We
strive to make our base sheet as bright/white as possible. Our coatings are
also white before OBAs are added. So as the OBAs "burn off", the coating
will become less bright, but if the remaining ingredients of the coating,
and the base sheet, are bright, the effect of the OBA's are not as
noticeable as they are on an off-white base sheet.

I hope this covers what we spoke of on the phone.

Diana York ~ Hawk Mountain Papers

Clearly this is a complex subject with no simple answers. It seems to me that in order to make a truly informed decision about a paper we should know the time frame for burn-off to occur, and to what degree whiteness and brightness will be affected. Considering the information uncovered so far, it seems likely that the effects of burn-off will vary among different papers. I hope this article will generate some discussion and more research.

Addendum: Since the above was written I have spoken with more paper industry sources about this, and I brought up the fact that in the ISO specification for archival paper is the condition that it contains no OBAs. The responses were interesting. They either declined to comment or said the specification was out of date and needed to be updated to match modern technology. Nobody spoke in support of it. From these conversations I got a pretty clear sense that they feel the OBA issue is blown way out of proportion. It is frustrating not to be able to get a clear and definitive answer to the question, but apparently there is currently not wide agreement within the industry and everyone is tip-toeing around it. But if I read the tea leaves correctly there seems to be a movement to downplay the issue.

About Alpha Cellulose Paper

There is a lot of discussion about alpha cellulose papers (made from purified wood pulp) and whether they are as "archival" as cotton papers. I have spent some time researching this, including paper makers' web sites and phone conversations with people directly involved in paper making as well as vendors who have spent years in the trade .

To make a long story short, the consensus seems to be that today's technology has advanced to the point that these papers are equal in longevity to the cotton papers, but tradespeople are generally reluctant to make an issue of it because there is such huge resistance to the idea among the users. So they are content to make both kinds and give the users a choice without saying much. The superior longevity of cotton is considered a myth at this point, but they recognize that "cotton" still has marketing value.

Acknowledgements

Thanks very much to Diana York of Hawk Mountain Papers, Dick Clampitt of Red River Papers, Jim Doyle of Shades Of Paper, Wayne Connelly of Innova Art Ltd and John Edmunds of Futures Ltd for their kindness and generosity in sending paper samples, spending precious time on the phone, and patience with all my questions.

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