For almost two millennia, paper has served as the most easily accessible and readable medium to communicate ideas. Countless works of art, manuscripts and books bear witness to the development of humanity. All this belongs to us as our cultural heritage which forms the demand to preserve this art and information in good condition. To fulfil this multifarious aim with long-lasting results for the collection, with an efficiently use of small resources the need of information for the decision-making process is enormous.
The conservator needs data in order to take informed decisions on whether and how to treat an object or whether an object can be displayed. Whereas a collection manager wants to know what proportion of a collection is likely to degrade faster or what proportion of a collection is inaccessible to the general public due to low mechanical stability of paper. And the politicians need authoritative forecasts to plan budgets. In conclusion it is important to know the overall situation as well as the particular demand of a single object. In a collection of several millions items, how the information can be collected and how sustainable the data are?
Paper is made over the centuries from a wide variety of different sources: e.g. rags, straw, cotton, pulp, ground wood and bleached cellulose. For a long time the papers were made by hand and even in industrial age – each producer has its own secrets. The technology of paper production changed and with it for example the kind of sizing. Is start with surface sizing with gelatine, later was used the industrial acidic sizing with rosin/alum and now the production changed two decades ago to synthetic sizing or even to know sizing. Hundreds of different paper sorts are produced for different purposes and even if the paper would be produced identical it never will be the same.
Inhomogeneous composition as a consequence of using natural materials and comes along with a natural ageing processes in combination with different storage and environmental condition lead to a different behaviour over the time. Additional the intensity of use will influence the condition too. Regarding its complexity is the characterisation of paper in archives and libraries an enormous challenge.
Reference methods to describe the condition of paper were until now destructive or a least micro-destructive, needs technical knowledge and were often combined with a time-consuming sample preparation. In summary the costs to analyse one item are high and material from the items will be destroyed. Reasonable, instead to use reliable reference methods only a few very simple techniques are occasionally used in archives and libraries to assess the condition of a paper collection so far.
Visual assessment can be used to describe the apparently situation. Most common is it to look for yellowing, but how can be the condition detected if the paper itself is coloured like for drawings? Does human eyes can define objective under different light sources the condition via the colour of a paper? At least the method is non-destructive.
Often used is also to determination of the acidity of paper using pH electrodes or acid-base colour indicators. Together with the publishing date it gives an indication of the paper situation. However, if there are no additional information a decision about the priority for the deacidification can not be done on the condition itself. Additional it will lead to water stains or coloured marks in unique items.
Recommended to get additional more information about mechanical properties of the paper is still the double fold. Folding a corner of a page as many times as it takes for it to break off and counting the number of folds is highly destructive and doesn’t correspond with modern standards in conservation. This technique is not suitable for valuable objects. In analysis of cultural heritage objects, destructive analysis is rarely acceptable.
As an alternative to traditional methods, spectroscopic methods can be reagent-free, fast and non-destructive. The SurveNIR team chose to combine near infrared spectrometry (NIR) with chemometrics (advanced statistical data analysis) to obtain a powerful multi-analytical tool.
The expectations for such a tool are enormous. The user wants information about the physical condition of the paper as well as decisions about accessibility of the item. Short-term preservations needs should be deduced and the tool should deliver reliable knowledge to set up long-term preservation strategies. Finally, arguments for budget plans and funding are required.
In preliminary studies Near Infrared were chosen as the most promising spectroscopic method. NIR is a scientific method and delivers reproducible results. NIR does not need a sample pre-treatment, can work with solid materials like paper, can be extremely fast, and is now available as portable instruments and it works non-destructive.
NIR spectra have a lower intensity and broader bands then Infrared spectra. The information in NIR spectra are normally interfere each other. Reasonable, that a mapping of peaks in NIR to individual vibrations is usually not possible. A visual analysis is therefore not successful. Since the NIR area contains a lot of overlapped information, mathematical and statistical methods are used to extract the required information. The so-called multivariate analysis is based on fast modern computers and can analyse with chemometrical models a certain NIR spectra in a matter of parts of a second.
However, the question to be solved was: Can the needed information be predicted from NIR spectra of paper?
To answer the question, a large collection almost 1400 historical paper samples were well characterised. Up to 15 properties per sample were determined: fibre furnish, acidity (pH), degree of polymerisation, cellulose molecular weight, tensile strength and tensile strength after folding, lignin content, gelatine content, rosin content, aluminium content, reducing carbonyl group content, ash content, presence of optical brighteners and grammage. From all these samples, more then 120.000 NIR-spectra were taken and then correlated with the reference data to obtain chemometric models.
Not countable numbers of hours were spent to collect data and NIR spectra to form a unique database. Finally, after calibration and validation of the chemometrical models SurveNIR is now able to measure books (stack mode) and single items (single mode). Primarily, SurveNIR will identify the kind of the paper. Four types of paper can be used: rag, bleached pulp, coated and ground wood papers. It allows a use of SurveNIR on a broad range of different items. Books, drawings, newspapers, archival materials and documents and also poster can be evaluated.
Available for each paper type are up to 9 additional chemical physical parameters: Acidity (pH), degree of polymerisation, molecular weight, tensile strength and tensile strength after folding, contents of lignin, protein, and rosin as well as the presence of optical brighteners.
The spectrometer is attached to user-friendly software. The program contains database functions to plan, to execute and to interpret surveys. Data can be imported and exported. The software provide a high functionality, one of them is the possibility to classify scientific data into categories regarding the different interest of each user. Additional the SurveNIR software can be used to combine a survey based on NIR with a common visual assessment. Within the software up to 50 so-called descriptive criteria can be defined by the customer with up to four categories for each criterion.
The software provides also extended option to report the results. They can be exported to Excel or can be calculated within SurveNIR. It is also possible to print separate evaluation protocols for each measured item separately.
Regarding the use on unique historical documents, a special task for the SurveNIR spectrometer was the safety of the evaluated items. Since normal available instruments could cause in warming up of the sample, evaporation of water and light irritations – the SurveNIR spectrometer was designed to avoid any possible side effects.
SurveNIR allows thereby evaluating large collections within a reasonable timeframe and on a scientific basis. It enables collection manager to plan efficient preservation strategies with an individual expertise. Since the structure of the software is flexible, the tool can be used for other approaches too.
SurveNIR was already performed in a number of significant European collections to proof the hard- and software. It could be shown that it has a very good impact. The tool was also used to support the research project “Identical Books”, founded by the Mellon Foundation. The identical books were evaluated with SurveNIR at the National Library of Wales Aberystwyth (NLW) and at the British Library London (BL). The lignin determination in both Libraries has shown a very agreement between both institutions which lead to the conclusion, that besides 2 items all other books can be defined as identical books.
In comparison of the margins of the identical books at NLW and BL we found not a significant difference for acidity and degree of polymerisation since the differences are within the standard deviation. However, as a trend are the margins at NLW a little bit less degraded and less acidic.
The NIR-development was initiated by ZFB Zentrum für Bucherhaltung GmbH Leipzig already in 2002. Within two regional projects, the first prototype NIR-paper rating tool was developed. From 2005-2008, 9 partners extended the idea of creating a usable tool within the SurveNIR project. The success of the 6th EC Framework Project SurveNIR prompted the company ZFB to decide on a new marketing strategy, in order to optimise the exploitation of the tool. This strategy involves the establishment of a spin-off company to commercialize the SurveNIR product. Dr. Dirk Lichtblau, who was the Director of Research & Development at ZFB, founded the company Lichtblau e.K. to market SurveNIR as a product and as a service, providing SurveNIR as a fully integrated collection surveying service including preparation, measurement and reporting.