State Archives in Dubrovnik, Croatia
Next to those in Vienna, Venice and Istanbul, State Archives in Dubrovnik is one of the most important historical sources for medieval and modern Mediterranean and Balkan history, founded in 1278. The Archives of the Republic of Dubrovnik are among the most important collections in the State Archives in Dubrovnik. The collection spans the period from 1022 to 1815 and consists of approximately 8.000 volumes, 100.000 single items and a collection of 15.000 Turkish documents.
The Republic of Dubrovnik (or Republic of Ragusa) was geographically located in Dalmatia, the southernmost tip of the present-day Croatia. It was founded in the 14th century and was conquered by Napoleon only in 1808. The archives mainly consist of parchment (which cannot be surveyed using the SurveNIR instrument) and of rag paper – manually produced from rags of linen and hemp, in the 18th and 19th centuries also from cotton. Such paper is very stabile, because it was produced using hard water, which contains a lot of dissolved hydrogencarbonates, which on drying turn into CaCO3 and MgCO3. These two compounds are only sparingly soluble, however, their solutions are mildly alkaline, which is just the right environment for cellulose, the main structural component of paper. After formation, the fresh sheets of paper were surface sized using gelatine, in order to prevent inks from running. Because of the method of production and because of the high quality fibres used in papermaking, rag papers are extremely stable and may survive several millennia in favourable conditions. Unless inks were used for writing and drawing, which lead to rapid paper corrosion, such as the infamous iron gall ink.
We surveyed a number of documents and were most interested in the pH (acidity) and degree of polymerisation of cellulose. While acidity is a very good indicator of paper stability, the DP - degree of polymerisation (number of glucose monomer units in the cellulosic macromolecule) tells us about the condition of the paper. The data show that paper is in general very stable (average pH of the collection is 8 ± 1) and in a good condition with high DP. It is usually assumed that paper with cellulose with DP lower than 400 is critically unstable. It is also of interest to note that there is no evident trend according to the age of paper, which indicates that the storage conditions have been favourable.
In the Archives, however, it is not the paper that is in a worrying condition, it is the ink. The acidic and iron-containing ink is very corrosive and leads to rapid degradation of paper written with such an ink and the lifetime of such objects can be reduced by a factor of ten or more. The SurveNIR software enables us to survey the condition of inks visually. In order to do so, the following four categories were defined prior to the category by the collection manager:
Category 1 (GOOD): no or slight discolouration at inked areas visible on the verso of the page. Documents with first indications of ink corrosion are physically stable; they do not need any intervention, but they should be inspected in regular intervals.
Category 2 (FAIR): partly dark brown discolouration at inked areas on the verso of the page – no mechanical damage. These documents need a conservation treatment or at least inspection in regular intervals.
Category 3 (POOR): intensive brown discolouration and mechanical damage (cracks) at the inked areas. These documents need conservation treatment.
Category 4 (CRITICAL): losses of the parts of the document due to the cracks at the inked areas. Most of these documents usually require chemical treatment against ink corrosion as well as stabilisation of the paper by whatever method.
The survey showed that most documents fall into category 1 and 2 (88%), however, 6% are in the most endangered category 4 (critical).