INHERENT VICE: STRUCTURES
In the previous section, you considered inherent vice within the component materials of paper-based collections. In this section, you will build on that knowledge as you consider several types of composite structures that are found in paper-based collections. These include bookbindings, photographic prints, and various types of reproductions. In these objects, the various component materials interact with each other (and sometimes with other nearby objects) to create additional vulnerabilities.
The basic form of the book has not changed fundamentally over the centuries, but changes in the materials and methods used in bookbinding have sometimes compromised the quality of the resulting bound volumes.
The earliest books were in roll form, made from papyrus. As vellum (which is more flexible than papyrus) began to be more commonly used, the practice of folding sheets and fastening them together began. Gradually the process of binding that is still used today was developed: individual folded signatures were sewn through the fold, then the signatures were attached to each other by sewing them to cords placed at right angles to the folded signatures. These cords, usually hemp cord or linen tape, were laced into the boards. Covered with protective material (e.g., leather, parchment, papers, and/or bookcloth), boards were added to protect the pages. Ideally, a binding should be strong and flexible, so that the book opens completely and the pages lay flat.
For brief illustrations of the terms used to refer to the different parts of a book, see the Dartmouth College Preservation Service's A Simple Book Repair Manual website.
Decline in Binding Quality
During the latter half of the 19th century and much of the 20th century, poor quality paper and boards were used for book construction. Wooden boards were replaced by various types of boards made from compressed paper pulp that become acidic over time. Many modern bookcloths (woven fabrics that contain pigments and sizes) used as coverings fade easily and are vulnerable to attack by insects or mold. Adhesives used in binding are also often unstable. Sometimes different parts of a book respond differently to changes in the environment, causing distortion.
Changes in binding methods also contributed to a decline in binding quality. Gradually, hand-sewing of books decreased in favor of machine sewing. Books that are machine oversewn rather than sewn through the fold do not open well, and their pages tear easily if they become brittle. Inexpensive case bindings, in which the cover is prepared separately and then attached to the textblock by gluing the endsheet to the case, are less durable than traditional bindings in which the cords were laced in to the cover or slipped into a split in the cover board and adhered (known as a split board structure). Perfect bindings (in which the pages are attached to each other with adhesive rather than sewn) often fail. Pages or entire sections of the book may fall out.
To see illustrations of common types of bindings, visit the Australian Heritage Collections Council's Collections website to download Chapter 1 - Caring for Cultural Material (PDF) and review "Types of Bindings" on pages 56-59. Think about the variety of bindings that you have within your own collections.
Beginning in the late 18th century, various reproduction methods began to replace hand copying of important documents. In the late 19th century, copying options were expanded and copying of original architectural drawings, plans, and maps became common. Objects produced using some of these copying processes deteriorate more quickly than others, and some have detrimental effects on other collections if they are stored together. Therefore, identifying particular processes is crucial in making storage and other preservation decisions for these materials.
A complete review of all copying processes is beyond the scope of this lesson, but a few of the most common are described here.
Letter copying process—Invented in 1780, this involved writing letters with a copying pencil and then pressing them against water-dampened thin tissue with a screw press. This process became popular in the 1850s and was used into the 1950s.
Hectograph process—This process, which became popular in the late 1800s, used aniline ink (usually purple or blue) and was used both for copying documents and architectural drawings. Writing was transferred to a gelatin pad from which copies were made. Various other processes for copying documents (e.g., mimeographs, Photostat, spirit duplicating) were invented in the late 19th and early 20th centuries. Many of these were not stable. See Luis Nadeau's Office Copying and Printing Processes (PDF) for a summary of processes.
Blueprints—Invented in 1871, this process was used primarily to copy architectural drawings, plans, and maps. A translucent original was placed over sensitized paper containing iron salts, and then exposed to light. After exposure, the original was removed and the copy was washed to remove the unexposed compounds under the lines of the original drawing. The result was an image of white lines on a blue background. Blueprints are sensitive to alkaline environments, and light exposure. Similar processes include Vandyke prints (which are sensitive to sulphur and other pollutants and often brittle), and Ferrogallic prints (which are alkaline and light sensitive and can stain adjacent prints).
Diazotypes—This process became popular in the 1920s, and by the 1950s it was used to copy office records as well as maps, drawings, and plans. A translucent original was placed on paper coated with diazonium salts; this was exposed to ultraviolet light, which attacked the salts and turned the exposed area off-white. Depending on the specific type of compound used on the paper, the lines on diazo prints can be various colors. Diazo prints are often processed using ammonia, which causes them to give off alkaline vapors that may harm other materials. The residual chemicals remaining in the print also cause oxidation and discoloration of the print itself, particularly on the edges. Sepia prints, a type of diazo print, can create greasy stains or pink stains on adjacent materials. Diazo prints are light sensitive.
Electrostatic copying—Also known as xerography, this technology was introduced in the late 1940s and became popular in the 1960s. It makes a copy of the original by forming an image with toner powder using an electrostatic charge and fusing the image to paper using a solvent, heat, or light. This is the most common copying process used today. If electrostatic copies are made on good quality paper and well-bonded to the paper, they are very stable. However, electrostatic copies of maps or plans made on matte or transparent Mylar are not permanent because the toner does not bond well to the Mylar.
See Lois Olcott Price's The Fabrication of Architectural Drawings to 1950 for more information on reproduction methods for architectural drawings and other materials.