With the term conservation, measures for the preservation and restoration of documents and artifacts in archives, museums and libraries are summarized.
Archives, museums and libraries store documents and artifacts that form the cultural and historical memory of the place where they are located: City chronicles, baptismal registers, court records, archaeological finds, historical journals, original manuscripts of musical and literary works, artistic sketches and prints, photographs, and film reels represent just a few examples of archival and custodial materials worthy of protection. To preserve it, it is necessary to counteract the natural processes of decay to which all materials are subject. The totality of all measures to preserve and restore these pieces is called preservation.
Damage assessment, damage patterns and damage prevention
Depending on their type, stored objects are subject to a variety of different decay processes - a distinction is made here between endogenous damage (caused by the chemical composition of the object) and exogenous damage (caused by external factors). The latter includes not only unforeseeable catastrophes, but also processes caused by incorrect storage and handling.
In archives and libraries, where most documents are made of paper, the most common type of damage is the so-called paper corrosion or acid corrosion, the decay of documents caused by acids contained in the paper. It affects most papers produced between 1800 and 2000, as their cellulose was often derived from wood and they were produced with the addition of alum. Ink erosion is caused by ink made from gall apples, whose high tannin content damages the paper - this often affects paper made in the 18th century or earlier.
Damage from improper storage and handling includes: spine breakage, damage from stickers, stamps, rusting staples, tape and post-its, mold, soiling due to lack of dust protection, yellowing or decay from exposure to strong light. Excessive humidity can promote rust or mold and provide favorable living conditions for pests.
Less frequent, but all the more devastating, are catastrophes such as fires (including water damage caused by extinguishing water) and mechanical damage - such as the collapse of the Cologne City Archive.
Museum storage facilities face similar challenges. Here, too, many pieces consist of organic material and are susceptible to pests, UV radiation, and sharp fluctuations in temperature and humidity - and thus to stress cracking, mold, and contamination.
Preventive conservation includes all measures that are intended to delay the deterioration and the need for restoration of documents as far as possible - also for cost reasons. These include proper storage and use, control of the room climate, protection against pests, fire and theft.
Preventive deacidification of lignin-containing papers is of particular importance. Because the problem affects so many documents, various techniques have been developed for individual as well as mass deacidification:
Ideal storage conditions in repositories and archives vary depending on the material, but usually tend toward cool, dark, dry, and clean storage. Appropriate climate control technology can help regulate conditions effectively and keep temperature and humidity levels approximately constant. Packaging protects against dust and pests, but must itself remain sufficiently stable over time - plastic, for example, must not contain a plasticizer that could leak out and damage the piece.
Access to fragile pieces must be regulated, and sensitive exhibits in museums should only be displayed for limited periods of time. Older books should only be opened to a maximum of 90° to avoid breaking the spine, and should only be touched with gloves. The specialist staff of the relevant archive or depot must inform visitors about the proper use of the documents, and if necessary also supervise or handle them themselves.
Conservation and restoration
Conservation means stopping the deterioration process of an object, while restoration means improving its condition. Restoration is considered when the document is very valuable or already severely damaged, or when it is to be prepared for presentation purposes or stabilized. It is significantly more cost-intensive than mere prevention. The type and extent of restoration depends on a number of factors - the material involved, the extent of the damage, the desired final condition. Objects made of paper, for example, are freeze-dried, applied to supportive backing material, and cleaned of dirt and mold, as needed. Paper splitting is sometimes used as a rare, expensive and invasive, but very effective method.
Increasingly, documents are being digitally preserved, for example when the information they contain is more valuable or historically significant than the material carrier itself and would be too costly to preserve, or when it becomes apparent that its deterioration can no longer be averted. Digital storage has the advantage of allowing access to the information contained in the document by far larger groups of people without endangering the original; digital copies can also be post-processed for better readability.