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Conservation Conversations // Another Look at Su-Su

November 15, 2014 by Erin Fletcher

Earlier this year, as part of the Conservation Conversations column, Lauren Schott wrote an article on su-su, which highlighted the steps to creating this alternative matter for toning materials as part of the conservation treatment. Also referred to as paper dirt or paper extract, I was first introduced to this alternative toning pigment at North Bennet Street School by my instructor Martha Kearsley. Later on, I used it while interning at the Boston Public Library, just as Lauren did the following year during her internship.

Conservation is a science and therefore it evolves as our understanding of it grows through research, experiments, discussions and time. John O’Regan recently brought the following article to my attention, which he found through CoOL (Conservation OnLine). In 2008, Erin Gordon of Queen’s University wrote Comparing Paper Extract to Traditional Toning Materials. Erin’s introduction to paper extract came during a workshop conducted by Renate Mesmer, Head of Conservation at the Folger Shakespeare Library in Washington, D.C. The information Renate presented was largely based on an article by Piers Townshend, Head of Paper Conservation at the Tate Conservation Department. Interestingly, this is the same article Lauren cites in her post as further reading on the subject.

Erin’s paper, as the title suggests, is based on her research conducted for the purpose of her studies in the Master of Art Conservation program at Queen’s University. If you are interested in knowing the science behind paper extract and other toning materials, I suggest you read through Erin’s paper. But those of you who are interested in reading the exciting conclusions Erin found right now, well here it is:

Paper extract has some positive characteristics. Paper extract is transparent and matches the tone of aged paper exactly. It absorbs into the paper substrate and maintains the paper’s matte appearance. Paper extract is more lightfast than tea and it is the most reversible of all the materials tested. Another advantage to paper extract may be that a colour shift as the repair ages may not be as visible. As shown in the aging trials, watercolour and acrylic both faded. After a few years when the surrounding paper has aged, but the repair has faded, these repaired areas will become quite apparent and will likely need to be re-done. The use of paper extract may prevent this dramatic colour shift.
These characteristics make paper extract a very attractive material to use for toning. Before choosing paper extract an important result of this investigation must not be overlooked. Paper extract degrades the paper substrate upon accelerated aging. The paper samples became more brittle and were significantly discoloured after artificial aging. According to the analysis done to the paper extract materials and then paper sources of the extract, the main culprit behind the deterioration upon aging seems to be lignin. Half the papers used as the raw material for the extract tested positive for lignin. The GC-MS results found a high abundance of lignin and its degradation products. Although the results show the content of lignin in the paper extract is contributing to the degradation of the samples during aging, there is a notable improvement in folding endurance and discolouration when the alkalized extract results are compared to the non- alkalized extract results. Further research should be conducted to test whether an adequate alkaline buffer can be added to the extract to make it archival or to test whether the extract can be applied to material that has been de-acidified with an alkaline buffer. Extract made from paper that is lignin free should also be tested to compare artificial aging results with the lignin containing sample results. After analyzing the results of this research, the conclusion can be made that paper extract is not the best choice for a toning material, as paper extract has been shown to degrade the paper substrate with accelerated aging. Although having better aging characteristics than tea, a commonly used toning material, the best choice remains to be either watercolour or acrylic paint.
Gordon, ANAGPIC 2008, 19-20

So the point of this post, is not to claim that Lauren or anyone using su-su is wrong in their methods (because it might be the most appropriate). But that as professions in the field of conservation, there is a responsibility to understand the positive and negative consequences of the treatments and materials employed (and how those factors may change over time). The pros and cons must be weighed for each object individually, while keeping in consideration its history, its function and its future. Understanding our materials and why we choose to bind, rebind or repair a book in a certain way must continually be reaccessed.

I’ve targeted the conservator throughout this post, but I don’t believe that professional bookbinders are free of this task either. As is the case with most professions, we grow as an industry and individual through consistent research, experimentation and discussion.

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  • My name is Erin Fletcher, owner and bookbinder of Herringbone Bindery in Boston. Flash of the Hand is a space where I share my process and inspirations.
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