Conserving, Preserving, and Restoring Your Heritage. Kennis KimЧитать онлайн книгу.
for most two-dimensional works can be divided into:
1. Issues with the support, such as the paper or parchment.
2. Problems with whatever medium was applied to the support, such as ink, charcoal, or pencil. Paper supports are very prone to acid deterioration. Paper is made from cellulose extracted from wood pulp by strong chemicals. The paper produced contains acids left over from the pulping process. Additional acids build up in paper as the lignin in the pulp deteriorates with age, and with exposure to the sulphuric acid that is produced when the moisture in the air contacts sulphur dioxide from coal and petroleum combustion. Art and documents discolour and become brittle as these acids cause deterioration of the molecular structure.
Parchment and other hides are naturally very strong and can withstand a great deal of manipulation due to their composition. During the preparation of hides, alkaline substances are applied making the sheets resistant to acid deterioration. The greatest preservation issues relate to their extreme sensitivity to moisture. Hides often illustrate varying degrees of buckling and deformations due to changes in the relative humidity. This buckling can be so severe that it interferes with the aesthetics of the piece.
Paper, too, can buckle or become deformed due to changes in relative humidity, but the more troublesome risk of exposing paper to high humidity is foxing. Foxing refers to small brown spots that form on paper that can be visually disturbing and result in small holes. It is thought that foxing is a mould growth as a result of impurities in the structure of the paper or the sizing material that was applied to the paper during production.
An exposure to water or 68–70 percent RH will allow mould to attack the sizing applied to the paper, the medium, or the structure of the paper (cellulose), parchment, or vellum. Mould is a health hazard and it disfigures and visually alters artifacts.
Other problems common to paper and parchment supports include discolouration, yellowing, darkening from light exposure, fading, or colour change due to light exposure, darkening due to exposure to acidic materials, matt burn, liquid staining, oil staining (frequently from fingerprints), media-induced staining, adhesive staining, adhesive residue, creases, folds, tears, holes, surface abrasion and fibre loss, pinholes, flyspecks (which appear as dark irregular dots), insect damage, attachment to inadequate or damaging support materials, applied adhesive, or damage as a result of previous inappropriate repairs.
Table 1: Environmental Recommendations for Paper-Based Artifacts
The media used to produce documents and works of art on paper can be just as prone to deterioration as the paper supporting them. Although graphite and pencil are relatively stable, pastels, charcoal, and chalk are all powdery and smudge easily. There are commercially available fixatives, but they should probably be avoided as they can change the colour of the pigments and trap dirt on the surface; some have been linked to deterioration of the paper supports. It is common for twentieth-century blue and black inks of fountain, ballpoint, and felt-tipped pens to fade to a brown colour because the inks were made from dyes rather than pigments. Some of these inks are so unstable they even fade when in dark storage. Older inks also have problems, especially early twentieth-century iron-gall ink. The gallic acid reacts with the iron resulting in corrosion that destroys the paper on which the ink was written. This appears like burns and holes in the paper.
Tempera and other paints applied to a sheet of paper or parchment can begin to flake or powder, resulting in losses from the image layer on the support. When the support, whether paper or parchment, is not handled properly when moved, it flexes and bends causing the more rigid applied media to flake off. Movement in the form of small expansions and contractions also occur when there are changes in the relative humidity. This too results in losses of the applied media.
Specific rules for handling various artifacts are given in Appendix 4: General Rules for Handling and Moving Artifacts and Works of Art, but here are some general guidelines to remember:
• Try not to directly touch the artifacts. The oils occurring naturally on your skin can damage and stain your treasures.
• Handle items with mount and matt boards by the supporting board.
• Handling un-mounted sheets by lifting them by the upper corners so that they hang freely without bending.
• Wear gloves when working with artifacts. White cotton gloves are recommended.
• Always place artifacts on a clean and level surface.
Preventative Conservation
The first step in preservation is to always thoroughly examine your artifact for damage and potential problems and check the overall structural stability of the work. One of the most common and helpful things that can be done at home is a very light, dry surface cleaning to reduce the amount of dust, fibres, and other foreign material that may have collected on the surface. Never attempt to clean brittle papers or powdery media, such as pastels, chalk, charcoal, or painted surfaces.
Surface dirt should be removed not only to improve the aesthetic appearance of the piece but also to eliminate a hazard. Dirt is abrasive, it can be acidic, and it holds moisture, which promotes the growth of mould spores. If your work can tolerate a light cleaning, you will need a very soft natural bristled brush, an air bulb (either the type used for a baby’s nose or those sold at photographic supply stores), and a drafting brush.
Wearing white cotton gloves, you should begin by gently blowing away any loose surface dirt with the air bulb. Follow this by brushing lightly with the soft natural bristled brush. Begin brushing from the centre of the object and work toward the edges. Use very light pressure; the paper should not move with your brush strokes. As dirt and dust accumulate around the edge of your artifact and on your work surface, remove it using the drafting brush. Once the surface dirt has been reduced, the artifact can be prepared for storage or display.
Storage and Display
Where items will be stored is as important as the method and materials for storage. Roofs leak, basements flood, and the temperature in attics fluctuates greatly day to night and through the seasons. Careful consideration should be given to the type of artifact to be stored and the conditions of storage. In bad conditions, deterioration can happen rapidly and with heart-breaking consequences.
Once you have determined a location for storage, chose the storage method and materials. Print files or drawers available from office, art, and drafting suppliers are very space efficient. Metal files with a baked-on finish are preferable to wood because wood is acidic and acid contamination can be transferred to your stored artifacts, resulting in damage.
Solander boxes or storage boxes made from acid-free corrugated board, acid-free and lignin-free box boards (TrueCore), or corrugated copolymer (Coroplast) can be arranged within the metal file drawers to help organize your holdings by size, subject, or medium. Ideally, artifacts should be matted prior to storage, but this is very costly.
When stacking matted, mounted, or loose artifacts, place separation sheets between each work. There are many materials that can be used to separate the artifacts: glassine, interleafing tissue, Permalife paper, Melinex (clear polyester film), or PermaDur to name a few. Each has advantages and disadvantages and you should research which is best for your collection. Table 2: Papers and Characteristics offers a limited comparison of some of the archival papers available. Folders made of acid-free stock are another alternative for sorting your collection and separating works within file drawers or boxes.
Damaged items can be protected by placing the items in a folder or an envelope or by encapsulating the artifact between two sheets of clear polyester film (Melinex — see Appendix 5: Encapsulation Process). Do not confuse encapsulation in polyester film with lamination.