Experimental design
For the purpose of the case study, a set of mock documents (bound, i.e. books, and unbound, i.e. loose sheets) made from historic paper of known chemical and mechanical properties were subjected to physical challenges representative of handling that might be typical of a historic archive or library collection. After rounds of physical challenges (ten instances of handling each), the documents were assessed for changes to their physical state, i.e. deterioration. Of particular interest were tears and missing pieces, as their influence on user evaluation of fitness for use was assessed in our previous research [11].
The experimental design was expected to yield the following types of data:
-
1.
The number or degree of changes per challenge, i.e. ten instances of handling (e.g. X number of large or small tears, Y number of large or small missing pieces).
-
2.
Given that the challenges were intended to be representative of handling in a real library or archival setting, and the frequency of use in archives/libraries is generally known, then the above data can be converted to expected number of changes per period of time.
-
3.
The above data and analysis was obtained for bound and unbound documents and was used to explore the comparison between a typical library document and a typical archival folder.
The SurveNIR Reference Historic Paper Collection [18] was used as the source of paper. The textbooks, guidebooks and fiction books range from mid-nineteenth to mid-twentieth century, and are written in Slovenian, Croatian, Serbian, German and Italian and 25 were selected for the simulation study on the basis of the DP of the paper in the books (~300–1000) and the amount of paper available, as both a bound and an unbound object had to be produced using the same paper. The paper was characterised in terms of variables such as molecular weight, DP, pH, fibre furnish and other properties, using traditional analytical techniques, such as viscometry for DP and cold extraction for pH [19]. Since some of the papers used in this study contained lignin and could not be dissolved in the solvent used for viscometry, their DP was determined using size exclusion chromatography by Morana RTD d.o.o. (Ivancna Gorica), following the previously described methodology [20]. The average uncertainty of DP determination was ~10 %, which included experimental and sampling uncertainties and results of this research need to be interpreted in light of this uncertainty.
It also needs to be clarified that all papers used in this study were made following the European papermaking practices of the time (rosin sizing), acidic and not coated. All were printed.
From among the total of 25 pairs of bound/unbound simulated objects, 4 were additionally degraded in HCl-enriched atmosphere at 80 °C overnight, in order to rapidly obtain highly brittle material. The DP of these papers was measured using the same technique as outlined in [19], following ISO 5351:2010. As this research is only concerned with the material state (measured in terms of DP) at the time of the experiment described in “Challenges”, previous environmental history (or indeed ultra-accelerated degradation in HCl-atmosphere) of the experimental papers is not of interest.
From each SurveNIR book, a 0.5–0.7 cm stack of paper (several sections) was rebound by a professional bookbinder (sections hand-sewn, spine glued with PVAc, hard binding on board, including an end paper, mull spine lining, fabric cover over spine, uncovered, with overhang, paper trimmed around the edges). This type of binding enabled all books to be comparable and data independent of binding type.
Most of the books had 6 sections, giving 48 sheets or 96 pages per document. For one book there was only enough paper to rebind 2 sections, giving 16 sheets or 32 pages. For two bound documents there was only enough paper to rebind 3 sections, giving 24 sheets or 48 pages.
For each of the 25 bound documents, there was a matching document made of unbound paper from the same SurveNIR sample book, with sections cut along the inner margin to create sets of loose sheets, which were additionally trimmed around the borders. Using guidance on storage of loose-sheet documents provided by The UK National Archives, Kew (TNA), the unbound documents have been placed in four flap folders. The unbound documents and folders have been labelled with their original SurveNIR code and the pages have been renumbered. Figure 1 shows some examples.
Eight sets of three pairs (bound and unbound, same paper) of documents were compiled, with one pair of documents set aside as replacement if needed. In each set of three pairs there was a range of paper DP values (low, medium and high DP pairs) in order to avoid confounds of DP with any physical challenges.
Each set of documents was packaged in a large envelope that prevented wear and tear during transportation.
Challenges
The documents were subjected to blocks of physical challenges. Each challenge had the following components:
-
Packing.
-
Tasks performed by participants, involving transport to the challenge venue (office or home), unpacking, performing a task with each document, repacking and transport back to the lab.
-
Assessment of each document by the researcher–assessor.
For a block of physical tasks (i.e. a challenge) the aim was to subject each document to 10 instances of handling. A number of challenge cycles was conducted, mostly 9, representing 90 instances of handling. Each challenge on a given document was performed by a different participant. Their brief was to leaf through the document 10 times as if reading/searching for information. Some paper was too brittle and allowed for only 5 challenges before assessments of change became very onerous due the extent of physical degradation (Fig. 2).
To simulate reading with handling, participants were asked to leaf through an entire document in a short space of time. It took about 1–2 h to complete the tasks for a set of documents. The 9 participants were members of staff, researchers and volunteers (non-experts) at UCL Institute for Sustainable Heritage.
To make the study as representative as possible, the participants were assigned to challenges using a random number generator. Additionally, in each challenge, a participant received three books and three archival folders with paper of low, medium and high DP. No participant was assigned the same object twice.
Wear and tear could also occur during transportation of documents within an institution. However, the characteristics of transport and handling occurring in real historic libraries and archives vary from institution to institution, and potentially within an institution. For example, an archival folder might be retrieved from the repository, used very briefly by a reader, and then returned to the repository on the same day. Another box might be retrieved and used intensively for a week before being returned to the repository. In addition, different parts of a collection are held in different locations and produced to different reading rooms. Because of this, potential mechanical deterioration between the challenges was avoided by packing the documents into sturdy envelopes.
Assessment
Assessment took place at the end of every block of physical challenges. The key measured features followed the elements of distress as discussed in Part I [11]: tears and missing pieces. These were classified according to size and location:
-
Small: tears of less than 5 mm from the edge of a sheet.
-
Medium: tears or missing pieces in the 5–20-mm boundary, or tears that affect the inner margin in a book (binding edge).
-
Large: tears or missing pieces that cross over the 20-mm boundary, within which text/images would be affected.
It is important to note that the assessment method used in this study is not ‘condition’ assessment [5] but rather a quantitative measure of physical change, specifically designed to enable categorisation in terms of the fitness of a document.
Since tears and missing pieces are caused by handling, their occurrence should be correlated with the mechanical properties of paper. Therefore the assessment measures are intended to be both indicators of use and sensitive to paper mechanical strength.
To avoid assessor bias, the assessment methods were developed and piloted in collaboration with several assessors and researchers initially. A number of books were independently assessed by two assessors on two occasions. To standardise the assessments, the following tools were developed:
-
Templates. These were necessary as the sheets were trimmed to remove any previous wear and tear, which was assumed to have an effect on the experiment. Two assessment templates were designed: a template for bound documents and a template for unbound documents, printed onto a transparency and placed over the sheet being assessed.
-
The template divides a sheet into several regions: A–H (Bound) and A–I (Unbound). These are overlaid on a 1-cm grid used for measuring the length of tears and the area of missing pieces. The red-dotted line marks the 5-mm boundary around the edge of a sheet (within which features are only counted). The solid red line represents a 2-cm margin (Fig. 3).
-
The template represents a typical sheet from a book based on measurements taken before rebinding (e.g. most bottom margins were >2 cm wide), but could be moved around in order to assess sheets of differing dimensions.
-
A template excel file was created to record the data and each spreadsheet had the following elements:
-
Sheet: features were recorded sheet by sheet.
-
Tears: tears around the edge of the sheet within the 5-mm boundary were counted (likely to be approximate); other tears were recorded individually (location, length, direction etc.). Since small tears can develop into large tears and large tears can lead to missing pieces and, therefore, the elimination of tears, changes in tear numbers could be positive as well as negative.
-
Missing pieces: similarly to tears, small missing pieces were counted and larger ones were described in detail, categorised and summed up.
Based on piloting, there was greater agreement between assessors about the location of a feature and whether the text area was affected, rather than finer details of features (e.g. whether a tear has affected the text and images in a document, rather than how long and in what direction the tear is). These are also likely to be the features most important to readers when assessing fitness for use [11]. Hence, these were the key measures used to describe change in the documents over time.
Following the pilot assessment phase, all changes (tears, missing pieces) in all document sets were assessed by the same researcher after each challenge.
Frequency of document use at the National Archives, Kew
Data on the frequency of use were made available by The National Archives, Kew, per bay (set of shelves) and not down to any greater detail, e.g. shelf, box or reference number. The data illustrate that yearly productions of individual documents would be expected to be very low, with 50 % of the c. 20,000 bays at Kew having documents produced from them between 1 and 10 times per year (Fig. 4).