Paper basics: Buffering

In alternative photographic processes, the choice of paper plays a crucial role in achieving a good print as well as in the archival quality and longevity of prints. Buffered and unbuffered papers are terms often encountered in this context. Some processes are fine with buffered papers and, in some processes, buffering will ruin the print.

Writer / Malin Fabbri
Photography / Malin Fabbri and John Brewer


Art paper on a shelfMost art papers today are buffered, and it may say so on the package. Labels that indicate papers are buffered are “acid free” and “archival”. If they are not buffered, it may say “unbuffered” or “no buffering”.

So, why do manufacturers buffer papers?

Buffering is included in papers to act as a buffer, counteracting natural acids in the environment to increase the longevity of the paper with the print itself or the matte or board it sits on. It has been shown that acids can attack photographic film supports and paper supports and that some acids can directly oxidize silver images (1, 2).

A pH of 7 is neutral; a value below is acidic and a higher value is considered alkaline. Acidity greatly accelerates the decay of papers and may make them brittle with time. Buffering is done using a compound to stabilise the pH value at an alkaline level to stop acids from degrading or ageing the paper. In an effort to put those all-important words “acid-free” on the packages, some producers have been adding buffers to paperboards made with acidic wood pulps. The result is that pH tests may show the paper is alkaline, while it may in fact contain acids (3).

How is buffering done?

Buffering is when calcium carbonate (chalk) is usually used to counteract acids and make the paper alkaline with a pH of above 7. Before this method was discovered, papers were buffered by using water from limestone aquifers. The buffering agent is added to the pulp to buffer, or counteract, natural acids in the environment to increase the longevity of the paper and stop it from turning yellow over time. It is often used in matting and mounting to prevent acid migration from the mounting material to the print.

buffering paper beakers
Photograph taken by Katrina Newbury at a workshop during the Pt/Pd Conservation conference in 2014 in Washington DC, organised by Connie McCabe at the National Gallery of Art.
The beaker in Mike’s right hand is a fresh green solution of pure Ammonium Iron(III) Oxalate (as used in his siderotype processes). The beaker in Mike’s left hand is the same with added chalk (calcium carbonate). Note the formation of a brown gungy precipitate of iron(III) hydroxide. That is what happens within buffered paper when chalk reacts with any iron(III) compound, to be hydrolysed by this alkali to form iron (III) hydroxide.

Buffering and alternative photographic processes

Buffering may sound like a good thing, but in printing processes such as cyanotype, prints can be harmed by alkalinity; so, unbuffered papers are best for most dye transfers and alternative photographic processes using iron in the chemistry, such as argyrotype, chrysotype, cyanotype, kallitype, platinotype, platinum prints and vandykes. Citing Mike Ware: “Chalk, which is hostile to the iron(III) chemistry, its alkalinity causing hydrolysis of the Fe(III) complex; moreover, with cyanotypes, it is directly destructive of the Prussian blue image substance, which is rapidly bleached at pH 9” (4).

An exception is pigment processes such as gum bichromates, carbon printing and casein prints as well as photomechanical processes such as intaglio printing and lithographic printing. This is also the case for framing or archiving prints.

Matting and archiving prints

Buffered papers are commonly employed in matting and mounting to provide a stable and pH-neutral environment for artworks. This helps prevent acid migration from the mounting materials to the artwork, preserving its integrity. This applies to “ordinary” photographs, but for alternative photographic processes sensitive to buffering, then unbuffered material should be used for matting and archiving. For example, the chemicals in cyanotypes may react badly to an alkaline environment.

How to test if a paper is buffered

There are a couple of ways to test the pH of a paper to determine if it will work or not—some easy, some a bit more complex.

  1. The absolutely easiest way to determine if a paper will work is simply to do a test print. This will show if it works or not.
  2. This tip I found in Christina Z. Anderson’s Cyanotype book; referring to Mark Nelson’s description of the New Cyanotype being the “canary in a coal mine”. Print a New Cyanotype using Mike Ware’s New cyanotype. If the paper is buffered, it will react badly and may be fogged, with the whites not clearing, or the print may have low contrast. 
  3. Use a pH test pen, such as an Abby or Lineco pen. Draw a line on the paper and if the line is yellow, the paper is acidic; if it is purple, it is neutral or alkaline. For artists using iron-based processes such as cyanotype, this is not a good method, since those artists need to know if the paper is alkaline (not acidic). It is not a foolproof test since both Arches Platine (a pH-neutral paper) and Canson Mixed Media (fully buffered of alkaline reserve) have been noted to give a purple reading.
  4. Some recommendations on the Internet suggest to add a drop of vinegar to the surface of the paper and listen for a fizz. I have tried on several papers which I know are buffered, but have not been able to make this work, even by tearing the paper in case the sizing stops the liquid.
  5. Others recommend the same as above but with Sulfamic acid which is a stronger chemical. Sulfamic acid can cause skin irritation, and serious eye irritation and is harmful to aquatic life, according to the MSDS sheet for Sulfamic acid. Be careful when using chemicals and take proper safety precautions. Where you have an option, always use less harmful chemicals.
  6. Submerging the paper in citric acid will produce bubbles on the surface, this I have tried and it works. See below.

How to de-buffer papers

You can de-buffer papers by soaking them in a citric acid bath or a sulfamic acid bath, but the easiest option is just to get papers that are not buffered and not deal with the extra work. If you decide to de-buffer, I strongly recommend using less harmful chemicals such as citric acid. One option to neutralize the effects of buffering is to add citric acid, sulfamic acid or vinegar to the final wash of a cyanotype, though the sulfamic acid treatment tends to degrade the paper surface and strength (5).

Submerging the entire paper in a solution of 5% citric acid will acidify the paper. A paper with a buffering agent will have bubbles appearing on the surface when dipped in citric acid. To make the paper suitable for iron processes such as cyanotype, leave the paper in the acid solution until the bubbles stop appearing.

acidifying hahnemuhle etching paper
A paper that is buffered and dipped in 5% citric acid will have bubbles appear on the surface. On this Hahnemuhle etching paper you can see the bubbles appear. The citric acid solution will acidify the paper making it suitable for iron processes such as cyanotype. Picture courtesy of John Brewer.

How to mix a 5% citric acid bath

Citric acid comes in powder form and is measured in grams, and water is of course a liquid and measured in mL or fl. oz. 

  • To make 500 mL mix 25,5 g citric acid (that is approximately 1.6 tablespoons) with 484 mL (16.3 fl. oz) of water (6).
  • To make 1000 mL double that to 51 g citric acid and 968 mL (32.7 fl. oz)  of water.

Simply dissolve the citric acid in the water by stirring it in.

Further reading and references

Sources:

  1. Adelstein, P. Z., J. M. Reilly, D. W. Nishimura, C. J. Erbland, and J. L. Bigourdan. 1995. Stability of cellulose ester base photographic film. Part 5, Recent findings. Society of Motion Picture and Television Engineers Journal 104:439-47.
  2. Carroll,J. E, and J. M. Calhoun. 1955. Effect of nitrogen oxide gases on processed safety film. Society of Motion Picture and Television Engineers Journal 64:501-7.
  3. “Effects of Enclosure Papers and Paperboards Containing Lignins on Photographic Image Stability” by Daniel M. Burge, James M. Reilly, Douglas W. Nishimura. Journal of the American Institute for Conservation, Vol. 41, No. 3 (Autumn – Winter, 2002), pp. 279-290. Published by The American Institute for Conservation of Historic & Artistic Works.
  4. Mike Ware, ‘Papermaking Additives Cause Degradation’, under ‘Technical Issues’ on Mike Ware’s website.
    https://www.mikeware.co.uk/mikeware/Paper_Additives.html
  5. Mike Ware, Cyanomicon available to read for free: Chapter 6, ‘Paper Characteristics’, § 6.4.1, pp. 176-179 of the iBook ‘Cyanomicon’
  6. Citric Acid Dilution Chart by RPC

If you are curious to learn more, here are a few links to check out:

 

Good luck printing!

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4 thoughts on “Paper basics: Buffering”

  1. Thank you. This was very informative. I have tried a few papers in the 5% solution, but so far no bubbles. But I will go through all the papers. Especially the very confusingly named ‘cartridge papers’ from Daler Rowney. Mike Ware’s Cyanomicon is most impressive. It will take some time to digest ……….

  2. Hi Rob,
    No… as explained in the articles, buffering is an agent that prolongs the life of the paper. Sizing is “glue” that keeps the liquid on the surface and prevents it from seeping though.

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