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  1. 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.

  2. Conservation Conversations // Su-Su

    July 29, 2014 by Lauren Schott

    Everyone who washes paper is familiar with the dramatic color transformation that takes place on the page after it is removed from its final bath. The evidence is left in the washing tanks; the water turns an unsavory yellowed color, and the paper is, to a degree, returned to its former glory.


    The concept of su-su is to harvest this colorant and use it to dull the often glaring white of repair tissues. It helps the eye transition over repairs to appreciate the elements of the original object, rather than the work that’s been done.

    My first introduction to su-su was a brief mention during a paper repair workshop. My instructor, while addressing a question concerning blending and color matching to make repairs less obvious, told the class about this paper color extract. “Dirt paint,” she casually called it. It sounded like something slightly magical and a little counterproductive, though she assured us it was effective and safe for the paper. (For more information on the science behind su-su, check out the article by Peirs Townsend titled “Toning with ‘Paper Extract’” in The Paper Conservator, Vol. 26 (2002) 21-26.)

    The concept of su-su lingered in my mind. It came up in conversation at my bindery every once in a while, so it seemed it was on everyone else’s minds, too. “Hey, you remember that su-su coloring? How does that work again?” and “Have you tried to make it yet?” But for one reason or another, it wasn’t until a few years later that I actually got to produce it myself.

    The first step in creating su-su is to gather acidic papers that won’t be missed. Scour what your library is discarding for those telltale brittle yellow pages. The conservation department where I was working when I made my su-su had been saving discarded covers, endpapers and other scraps for years just for this occasion.


    We filled a half gallon pot with acidic paper, breaking it up into small pieces as we went to increase surface area. After the pot was about three quarters full, we added water.


    We set the concoction on high heat over our small stove until it came to a boil. Once it was hot enough, we turned it down to a low simmer and let it cook for several hours, stirring occasionally. The water took on first that yellow color, then started to darken as it concentrated.


    After a few hours, we used tongs to remove the large pieces of pulp, and poured it through a strainer to remove the smaller particles. Then it was back to the stove for more simmering.


    The dark brown liquid soon cooked off to create a viscous syrup, which we stirred regularly to prevent burning, just as you would while cooking chocolate.


    We siphoned off the syrup into various shallow containers so the last bit of moisture would evaporate quickly. We mostly used the lids of small mason jars and some watercolor trays.


    Since several of our containers were made of plastic, we couldn’t put them back over the stove at this point. By this time, making the su-su had taken several hours of work, though often with on-and-off attention. We elected to allow nature to take its course and let the small cakes dehydrate on their own while we worked on other projects, although we did occasionally take a moment to help them along with the assistance of a hairdryer.

    This is the result.


    Though Townsend’s article claims that the resulting colorant is non-acidic, it’s always best to be sure of your medium before you use it on actual repairs. Test out the acidity of your result by painting the tint over a pH strip, and then take appropriate measures to balance out the pH of the tint before applying it to tissue. This batch was fairly neutral when tested, so I can use it without alteration.

    Su-su has become a regular part of my repairs. Whenever I pack a tool roll for conservational trips, it’s one of the first things to go in, right alongside my favorite bone folders and lifting knives. From my experience, a little goes a long way, and I anticipate this batch lasting me for quite a while.

  • 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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