Paper Conservation

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Statement of Purpose

Paper is frequently associated with natural history collection and herbaria specimens. It can be found in natural history collections in labels, tags, and many metadata documents, while it is in herbaria collections as a support and mounting material. Paper and paper-based products are used for storage (e.g., wrapping papers, cardboard boxes). It is also one of the favorite materials used by conservators during treatment (i.e., structural reinforcement, loss compensation). It can be used to fill the loss not only in paper but also other materials such as leather and fur. Therefore, it is essential for people working with natural history collections to know the fundamental properties of paper and patterns of its degradation. This section will also cover the overview of paper conservation methods.

Contributors

Magdalena Grenda-Kurmanow

Introduction: Paper as an element of natural history collections

Paper can be found in many different elements of natural history collections. Within herbaria, it can be found in:

  • (Bound) paper of the block
  • Paper of the binding, cardboards
  • (Other) paper of specimen sheets
  • Straps used for mounting
  • Labels
  • Interleaves
  • Wrapping papers
  • Specimen boxes (e.g., cardboard)
  • Archival material associated with specimens (e.g., printed and handwritten documents, photographs, etc.)
  • An addition to the object after conservation treatment (e.g., paper infills, mostly made of Japanese papers)

It is very common that one item may contain several kinds of papers, each of different properties. Such variety may influence the policy of storage and handling of the collection.

Definition of Paper

Paper is a layered structure of fibers lying almost parallelly to the surface of the mold used to form the paper. Fibers can bond without any adhesive, which is a characteristic feature of paper and papermaking process. Throughout the historic experiences and adjusting the production of paper to demands, many additives have been included in the production of paper, such as sizing agents, fillers, and dyes.

Permanent and Archival Papers

Permanent paper is a paper that should last at least several hundred years without significant deterioration under normal use and storage conditions in libraries and archives. The standard establishes criteria for coated and uncoated papers, defining required range of pH, tear resistance, alkaline reserve and acceptable lignin content. See the National Information Standards Organization (NISO) Standard for more information regarding the specific properties of such paper and the tests required to demonstrate these properties.

The symbol of compliance with the standard of permanence.

All publications printed on paper that meets this standard should carry the following information: 'This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).' The compliance symbol is the mathematical symbol denoting infinity set inside a circle[1].

ISO 9706 Standard (Information and documentation — Paper for documents — Requirements for permanence) describes requirements of aging behavior for the permanent paper, however aging tests are not obligatory. According to the standard, a permanent paper, after 24 days of aging in 80 Celsius degrees and 65% RH (relative humidity), should retain 80% of its initial durability.

Archival paper The standard for archival paper is ISO 11108 (Information and documentation — Archival paper — Requirements for permanence and durability) Archival paper is a highly durable paper for special purposes. It should be used for publications of historic, legal or other significant value. This paper should be made from cotton, cotton linters, hemp or flax, but may contain a minor fraction of fully bleached chemical pulp. In addition to the requirements listed in ISO 9706, the standard for archival papers also describes a minimal folding endurance. There is no compliance symbol for archival papers in ISO 11108, but it's emphasized that every archival paper meets the ISO 9706 standard and may carry the same information as in standard for permanence. According to requirements, archival papers are more durable than permanent papers and can withstand more handling. See Labeling_Natural_History_Collections#Paper for additional information on specimen labels.

Highlights in the history of papermaking

The beginning of papermaking originates from China. Traditionally, the invention of paper is assigned to Tsai Lun, the court official, who presented the report on papermaking in 105 CE to the emperor. He probably gathered state-of-the-art papermaking experiences from the country. His also introduced the paper mold, which enabled the production of fine sheets of paper by ‘sieving' fiber from the water suspension of fibers in a large basin.

Paper in the time of Tsai Lun was composed of the fibers processed from the bark of trees, hemp waste, old rags and fishnets[2]. The source material of fibers was washed in warm water, cut into small pieces and boiled in water with wood ash (e.g., potash, K2CO3). Then the fibers were washed again, cleaned and beaten to achieve single strands. The fiber pulp was added to the water, and then the paper sheet was formed in paper mould simmered in the water suspension of fibers.

From China the craft of papermaking was transferred to Korea (4th century), Japan (7th century), Samarkand, Baghdad (8th century), Egypt (9th century), Spain (10th century) and the rest of Europe. Paper was first introduced in Italy, France and Germany, in the 12-13th century and later to England in the 14th century. In 1690 the first paper mill in America was established. Some milestones in the history of paper include:

  • 105 CE Tsai Lun ‘invented' paper (probably compiled state-of-the-art papermaking experiences and introduced the paper mould)
  • 8th century papermakers from Samarkand introduced paper mills
  • 13th century watermarks were invented in Fabriano, Italy
  • 13th century first sizing of paper in Europe, with animal glue. The introduction of sizing relates to the need of smooth structure, because of inks and geese feather as a writing tool
  • 1680 the invention of ‘Hollander' (beater) in the Netherlands, in the maceration of materials for paper making
  • 1757 James Whatman produced the wove paper- using wove wire in paper mould, leaving no wire pattern in the sheet structure
  • 1785-1789 Claude Louis Berthollet used chloride to bleach plant fibers
  • 1799 Louis Robert invented paper-machine, developed by Gamble in 1801 (Foudrinier Machine)
  • 1807 Moritz Friedrich Illig – sizing with potash alum KAl(SO4)2 (which proved to increase the acidity of the paper)
  • 1807 fillers added for the first time to paper to reduce the costs of paper production
  • 1845 first groundwood paper produced in Germany (patent by Friedrich Gottlob Keller in 1840)
  • 1851 Hugh Burgess and Charles Watt started production of chemical wood pulp, cleaned with NaOH ‘sodium method'
  • 1866 sulfite method of wood pulp production; 1884 sulfate method of wood pulp production

Fibers Used in Papermaking

European paper was processed from rags made with the following plant fibers until the 19th century: flax, cotton, hemp and sometimes jute fibers. These are all long-fiber plants. In Japan, the most common papermaking plants are kōzo (paper mulberry), and also gampi and mitsumata.

Today paper is made mostly of wood pulp, processed from both coniferous and deciduous trees. Wood was used first in the papermaking in 19th (1845) century as a mechanically ground wood. Groundwood papers contain high levels of lignin, whereas the production of wood pulp includes chemical removal of lignin. The presence of lignin results in discoloration and darkening of paper, particularly if it's exposed to light and heat. It also causes embrittlement of the paper structure.

Considerations Regarding Removal/Replacement of Historical Papers

Historical papers are sometimes considered for removal or replacement due to their poor physical condition (e.g., tears, other mechanical damage) or pesticide contamination.[3] From the conservator's and historian's point of view, it is a very undesirable situation. Original papers may contain valuable information about the provenance of the object. The analysis of the grain of paper, its fiber structure, the pattern of the paper mold, and the presence and pattern of a watermark can result in a detailed identification of the object. It also provides additional information on the significance of the object, how the specimens were prepared, what could be the approach or material status of the collector, etc. Information is complex, being included on handwritten paper notes, labels and any other traces one can find on the paper support. Removal of old historic paper may deprive the object of integrity and historic and informational coherence. Also, a paper from before 1845 (when the first groundwood paper was produced), made of good quality rags, contains long fibers of cellulose and may have quality that is at least as good as contemporary archival-quality paper.

Conservation treatment of the original paper can deal with most of the damage, enabling the object for safe storage and handling while saving the original substance and features of the treated paper.

References

  1. National Information Standards Organization (NISO). Permanence of Paper for Publications and Documents in Libraries and Archives ANSI/NISO Z39.48-1992 (R2009). Bethesda, MD: NISO Press, 1997. [1]
  2. Hunter, D. 1978. Papermaking: The History and Technique of an Ancient Craft. Dover Publications, F First Dover Edition edition.
  3. Purewal, V. J. 2012. Novel Detection and Removal of Hazardous Biocide Residues Historically Applied to Herbaria. PhD thesis at University of Lincoln.[2]