Conservation and restoration of parchment
Throughout Europe, parchment was the primary writing substrate from its development in the 2nd century BCE through the Middle Ages, though it is used through the present day for various official documents.
[2] Parchment is also highly hygroscopic in nature, meaning that changes in relative humidity can cause irreversible variations to its structural makeup.
Prolonged exposure to alkali, like in parchment liming process, changes the amino acids, consequently dropping shrinkage temperatures as low as 55 °C (131 °F).
Historical coatings, which include chalk, egg whites and matte paint, must be taken into consideration as a meaningful part of the preservation and conservation plan.
[2] The manufacturing process, which removes the skin's natural fats and oils, means that parchment is more reactive to moisture and relative humidity than other skin-based material.
After being stretched, parchment has an inherent desire to revert to its original animal shape, especially if left unrestrained or exposed to repeated changes in relative humidity.
Visible hair follicle pattern, veining, scars, bruises and sometimes fat deposits all help confirm the animal origin of the material.
[2] Analytical testing, which involves removing a small piece of parchment, can be done by or under the supervision of a professional conservator-restorer to ensure positive identification.
[12] Direct water contact and excessive moisture in the environment can cause structural problems for parchment including: expansion of object; discoloration; alteration of surface coatings; gelatinization of skin; and realignment of fibers.
[14] Heat in excess of the ideal storage conditions can cause damage to collagen structure, irreversible contraction and alteration of surface materials in parchment objects.
[2] A consistent storage environment is crucial for the long-term stability of parchment, which is especially vulnerable to changes in humidity, temperature and other environmental factors.
The ideal storage and display environment is oxygen-free, as oxygen prevalence has been shown to react with collagen over time, leading to increased brittleness of parchment.
Oxygen-free storage and display cases are filled with inert gas as well as a chemical substance that reacts as an absorber if any stray oxygen leaks into the encasement.
[17] The hazards of specific treatments need to be weighed against the benefits, as many traditional liquid-based conservation techniques can pose risks to parchment.
Surface cleaning of parchment is typically completed using white vinyl erasers (solid and grated) and confined to areas where no media is present.
Water baths, which sometimes use neutral detergents or alcohol as additives, can be used to clean as well as prepare the parchment for stretching as part of the conservation process.
[19] Another wet cleaning method, which is especially useful for removing mold and mildew, uses a cotton swab covered in fluid, usually denatured alcohol, ethanol or saliva.
Correcting non-original splits, tears, perforations and losses in parchment requires careful consideration of its specific condition.
Parchment which has been accidentally exposed to excess moisture or water is extremely susceptible to mold, mechanical damage and irreversible dimensional changes.
[2] The United States Declaration of Independence, Constitution and the Bill of Rights, collectively known as the Charters of Freedom, were housed in metal and glass encasements, filled with helium gas, from 1952 to 2001.
[13] In 1982, the National Archives and Records Administration partnered with the Jet Propulsion Laboratory on a nine-year project which determined that the encasement glass was deteriorating.
[23] All the parchments were then installed into new titanium and aluminum encasements, developed by the National Institute of Standards and Technology, which are filled with inert argon gas.
