Medieval/Renaissance Documents: Restoring illuminations

One of the most significant problems suffered by illuminaries is paint flaking from the illuminations. Parchment expands and contracts, even with only very small fluctuations temperature and humidity. This, along with normal flexing of a page in a bound books, causes the paint in illuminations to flake. Paint that flakes in this manner is referred to as being friable--flaking or powdering. The process to restore thusly damaged illuminations is called consolidation. Consolidation aims to stop the flaking by applying a substance to the cracks in the paint to make them adhere to each other and the underlying surface. Many substances have been used as consolidating agents, including microcrystalline wax, beeswax mixed with dammar resin, and soluble nylon. These methods are no longer used because they are not stable long term. A currently accepted general method of consolidation involves painting a very dilute (approximately 1%) solution of leaf gelatin that is kept warm on a hot plate onto cracks in the paint after preparing the treated area with a coating of a small amount of ethanol. The leaf gelatin wicks into the cracks between the flakes, sealing them together and to the paint surface, preventing further losses of paint.



This method cannot be used on all types of pigments, however. White lead pigments, for example, are easily swollen or otherwise disturbed by most water-based consolidants, such as leaf gelatin. Methyl cellulose instead of gelatin is more appropriate for consolidating white lead. If the area of white lead is too instable, even the small amount of water in the cellulose may make the white lead swell too much. In this case, hydroxypropylcellulose or Klucel can be used. But cellulose consolidants also have their dangers. They can leave a shiny residue on the surface of the illumination and they can overpenetrate the parchment/vellum and darken the skin.

Other examples of difficult pigments to consolidate include orpiment, which cannot be treated with gelatin or other liquid consolidants containing water and/or alcohol because the bright yellow pigment becomes noticeably darker and more saturated in color when these adhesives are applied. Ultramarine and verdigris both flake in barely noticeable, sometimes microscopic bits of paint, that are easily picked up by a brush applying a gelatin-based consolidation medium, thus further damaging the illumination. An ultrasonic mister is better used to deliver the consolidation medium when working on or around these pigments. Misters spray the consolidant onto the illumination, eliminating the need to touch it.



Misters are difficult to use in bound manuscripts with writing on both sides of the parchment, however. (When used with paper for conservation, suctioning from the opposite side of the page is used to remove excess moisture. This is impossible with bound, two sided documents.) In response to this difficulty, in 1994, Dr. Robert Fuchs, a German scientist and conservationist, proposed using a commercially available machine called the Dosiergerät to applied consolidants to manuscripts without touching them. The Dosiergerät was originally made for precise gluing operations in the assembly of computers and other electronic equipment via a syringe.

Turner, Nancy. (1994). The Conservation of Medieval Manuscript Illuminations and the Question of Compensation. WAAC. 16(1), 21-22. Available
http://palimpsest.stanford.edu/waac/wn/wn16/wn16-1/wn16-108.html

Quandt, Abigail. (1996). Recent Developments in the Conservation of Parchment Manuscripts. The American Institute for Conservation Book and Paper Group Annual. 15, 14-15. Available http://aic.stanford.edu/sg/bpg/annual/v15/bp15-14.html