Since 1999 an extensive conservation measure has been running on the books of the DLA library: the books in question are subjected to the non-aqueous deacidification process in batches. In this process, the paper is impregnated with an alkaline reserve that counteracts future acid formation. Approximately 85 % of the library’s holdings can be deacidified, while 10 % of the holdings do not require deacidification. The exclusion criteria developed by the DLA show that a further 5% of the holdings are unsuitable for the selected deacidification process. The most important criterion for deacidification treatment is the condition of the paper. The DLA classifies this using a four grade scales (Fig. 1).
The data collected in the context of the volume deacidification project show that about 86 % of the volumes evaluated are suitable for deacidification treatment, while 14 % are not suitable for the chosen process. Among the materials that have already been deacidified, the majority of the materials evaluated so far (78% on average) can be categorised under Paper Condition Classes 1 and 2. These paper grades are potentially suitable for deacidification treatment and the process results in long-term deacidification and buffering of the paper.
Only about 6 % of the papers are already so severely damaged by acids (Class 3), that, while deacidification treatment is possible, it does not represent a sustainable measure as it cannot introduce a significant buffer. Approximately 10 % of the papers are categorised under Paper Condition Class 0 and do not require deacidification treatment.
Selection of the acidic papers is mainly carried out via a visual inspection, which requires a high degree of expertise and experience. In some cases, the assessment of the papers is supplemented with a spot test using the Abbey pH-Pen and visual classification of the colour change against a colour scale (Fig. 2).
The preservation of the heterogeneous original materials in the manuscript holdings of the DLA through the implementation of paper deacidification is currently being evaluated internally.