The restoration of historical paper documents
In the past few years the historical seismic recordings have acquired increasing importance in the scientific interpretation of the earthquakes of the past. Unfortunately, a number of factors have determined the dispersal, the destruction or the difficult conservation of the seismological material, in particular of the seismograms: a lack of space, fires, wars, floods, transfer of offices, etc. As a consequence, the need arose some time ago to deal with the problem of the proper conservation of this material in a systematic manner. The restoration laboratory acts upon the seismograms and the most interesting documents, which are particularly damaged and that risk definitively losing the information they contain.
Some reference guidelines have been established to deal with the most urgent problems.
The factors that need to be taken into account are the following:
- the constituent materials and manufacturing techniques (smoked, photographic, heat-sensitive paper, etc.)
- causes of deterioration (humidity, fungus attacks, tears, etc.)
- solutions by means of conservative intervention with the lowest possible impact.
Among the various types of decay, the damage most often detected in the seismograms and in the laboratory documents that we come to deal with are those of a biological kind: fungal attacks, those of a mechanical nature such as: tears, rubbing and consequent pigment loss, and those of a chemical-physical nature, such as: oxidation, peeling and yellowing of the fixatives.
The paper used for the recordings, often of poor quality, at times even reused, is either dry, fragile and ready to crumble at the slightest touch and is thusunworkable in the scanner, or on the contrary damp to the extent of showing wide mouldy stains and areas that are completely stuck or glued together. In these cases the laboratory tries to isolate the seismograms affected by fungal attack, as the spores, inert for years, could suddenly be activated in ambient with an uncontrolled level of humidity and spread to uncontaminated seismograms.
As the types of seismogram are highly varied, the causes of the decay are different and, as a consequence, so are the conservative intervention techniques which, from one time to the next, the restoration laboratory decides to adopt. By means of a series oftools and instruments and materials suited to the purpose, action is taken on the seismogram or the document by operating in the possible invasive manner.
The methylcellulose based on wheat starch water soluble in different percentages and the supporting materials, such as theJapanese tissue paper of different weights, have been specifically studied for this purpose. Unfortunately, often it is necessary to extend the restoration to the whole document when this has got tears and cuts all along the edge of different types of severity or when this is even subdivided into several pieces.