Below are some examples of how to use the database of damages (created between 2010 and 2012) to analyze the condition of parchment.
For example, based on the occurrence of damage and glass-like layers, it is possible to divide the collection of 2,306 document into three categories (Ill.1). The database also makes it possible to determine the condition based on the age of the parchment (Ill. 2).
Parchment from different centuries display different features in the way they endure, and knowing this can be useful as background information for practical conservation.
The endurance of parchment may differ based on the way that the parchment was formatted. Thus, for instance, differences appeared in the endurance of parchment when we compared similarly treated parchment, which was formatted into documents or bound into codices. As a result of the analysis, it turned out, for instance, that parchment from the 13th to 15th centuries had endured better when bound (Ill. 3).
By using the database on the condition and damages of parchment documents, it is possible to compile samples in order to analyze the issues that interested us related to organizing the preservation of the collection.
Thus, the analysis showed that most common damages throughout the centuries was the occurrence of stains of various origins. Stained documents comprise 68% of the entire collection. Stains, regardless of their origins, turned out to be closely correlated to the degradation of parchment, i.e. the appearance of glass-like layers, as well as the deterioration in the condition of the documents resulted therefrom. The linear correlation coefficient (p), that characterizes the relationship (Andmemasin, 24.03.2016) between the appearance of stains and glass-like layers, was between p=0.7 and 0.82, which alludes to a strong relationship between stains and the durability of the document. This impact is somewhat smaller (between p=0.55 and 0.62) in the documents that date back to before the 16th century, both sides of which are scrapped on both sides into thin and elastic parchment, without the upper grain layer.
The documents manufactured without removing the upper layer of the dermis and the hair follicles were in significantly poorer condition. The relationship between the appearance of hair follicles and glass-like layers were between p=0.5 and 0.7.
Taking into account the aforementioned correlation, it is possible to predict the number of documents with a preservation stability that is significantly greater (minimal risk of preservation) than the remaining documents.
For this purpose, samples of documents with a minimal risk of preservation by century were compiled from the same database. The documents that were chosen as the ones with minimal preservation risk were those without stains, biological damages, glass-like layers, hair follicles, and the physical integrity of which were included in condition 1. The number of documents from various centuries with minimal preservation risk are shown in ill. 4.
Such an analysis is important for determining the practical conservation needs and for planning the necessary resources. This hybrid parameter, i.e. minimal preservation risk, enables the number of archival documents to be determined in regard to which we can predict, with greater probability, that the properties of the parchment possess a higher level of stability. For obvious reasons, the number of documents with a minimal preservation risk is significantly smaller than the number of documents with condition 1 as classified by century.
One of the significant reasons for the surprisingly good durability of documents from the 13th and 14th centuries can be seen as the high work culture of the time and the continued use of the high-quality parchment manufacturing methods that had developed over the previous two to three centuries. The quality of the parchment was ensured by the selection of high-quality raw materials and parchment manufacturing procedures. During this period, the parchment that was prepared for writing was worked on both sides into a thin, elastic material, which was basically comprised of the long-lasting collagen-rich dermis. Splitting was often used to thin the skin, whereby the grain layer was also removed with the epidermis. This enabled super-thin (0.05 to 0.1 mm) vellum of uniform thickness (±10-20%) to be produced.
The significant deterioration of durability in the late 15th century and 16th century make have been directly related to the changes in parchment manufacturing methods and the selection of raw skins. In order to simplify the manufacture of parchment for use as documents, only one side of the skin – the one intended for writing – was processed completely during this period. Only the epidermis and the subcutaneous tissue was completely removed or split. The processing became sloppy. The physical harm caused by the processing and damage to the grain layer, along with the subsequent gelatinization of this layer significantly worsened the durability of the parchment. As a result, the parchment was considerably thicker, the chemical properties the skin fluctuated, and the entire surface of the skin was noticeably uneven.
The number large stains (78%) and physical damages on the parchment documents from the 16th century alludes indirectly to the unstable and historically complicated situation on the territory of Estonia.