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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Architectural reprography | 1/2 | https://en.wikipedia.org/wiki/Architectural_reprography | reference | science, encyclopedia | 2026-05-05T14:00:16.071892+00:00 | kb-cron |
Architectural reprography, the reprography of architectural drawings, covers a variety of technologies, media, and supports typically used to make multiple copies of original technical drawings and related records created by architects, landscape architects, engineers, surveyors, mapmakers and other professionals in building and engineering trades. Within the context of archival preservation, the custodians of architectural records must consider many aspects of identification and care when managing the artifactual nature of these materials. Storage containers, handling, paper and chemical compositions and interactions, ultraviolet light exposure, humidity, mold, and other agents of potential harm all interact to determine the longevity of these documents. As well, architectural reprographic drawings are often in very large formats, making storage and handling decisions especially complex.
== History == With the rise of the professionalized practice of western architecture in the second half of the 19th century, the field of architectural reprography—and the corresponding developments of photography and mass-produced wood-pulp paper—saw significant experiments and advances in technology. Beginning with the discovery of the cyanotype process in 1842, major refinements in blueprinting processes in the 1840s, through the widespread adoption of diazotype printing after World War II, the design profession turned to analog architectural reprography to create accurate, to-scale reproductions of original drawings created on tracing paper, vellum, and linen supports. These copies were typically used throughout the architect's own design process and also for distribution to clients, contractors, governmental agencies, and other interested parties. However, the integration of CAD—or Computer-Aided Design—over the last twenty-five years of design practice has made analog reprography far less common in the profession and more ephemeral in nature. For archivists, curators, librarians and other custodians of architectural records, traditional reprographic formats are now often seen as historic documents, with attendant needs for long-term care and conservation.
== Major processes == Both the underlying support—paper or plastic—and the image type are used to identify the specific processes used in architectural reprography. Between the late 19th century and the late 20th century, several processes emerged as the preferred methods, used for decades, while other less common processes were employed for shorter periods of time.
=== Blueprints ===
Also called a cyanotype. Developed in the 1840s by John Herschel, blueprinting uses a wet process to produce an image of white lines on a cyan or Prussian blue ground. To make a blueprint, a heavy paper (or more rarely drafting linen) support is impregnated with potassium ferricyanide and ferric ammonium, placed under a translucent original drawing, weighted with glass, and exposed to ultraviolet light. After sufficient light exposure, the glass and original drawing are removed and the blueprint paper is washed to reveal a negative image. This same process, using an intermediary reprographic drawing, could also be used to produce a positive blueprint—blue lines on a white ground—however, this more expensive and time-intensive method was far less commonly employed. The major disadvantages of the blueprint process, however, included paper distortions caused by the wet process which might render scale drawings less accurately, as well as the inability to make further copies from the blueprints. Nonetheless, for its efficiency and low cost, the blueprint process, further simplified and mechanized by the turn of the 20th century, became the most widely used reprographic process from the mid-19th century through the first half of the 20th century. In archival settings, because the process involves ammonium, the resulting prints should not be stored in contact with other papers that have a buffered reserve, nor should blueprints be de-acidified, as the resulting chemical interactions can cause irreversible image loss. Blueprints are also highly light-sensitive and should not be exposed to ultraviolet light for long periods of time.
=== Pellet prints === Invented in 1887 by Henry Pellet, the Pellet process uses a wet process to produce an image of cyan or Prussian blue lines on a white ground. Essentially, this process produces a positive image, while a blueprint produces a negative one. To make a Pellet print, a paper (or more rarely drafting linen) support is coated with ferric salts suspended in a gelatin emulsion, placed under a translucent original drawing, weighted with glass, and exposed to ultraviolet light. As with the blueprint process, after sufficient light exposure, the original drawing is removed, the paper washed in a ferrocyanide bath, and then rinsed in an acidic bath to reveal a positive image. This process required fewer steps than creating a positive blueprint, and was thus more widely employed during the late 19th and early 20th centuries. In an archival setting, Pellet prints should be treated and stored under the same conditions as blueprints.
=== Van Dyke prints === The Van Dyke process, invented by F. R. Van Dyke in 1901, created an intermediary print—a white line on a dark brown ground—that could be used in any of several other processes, such as blueprinting, to create a positive print, i.e. a dark line on a light ground. Using a translucent vellum support, the paper was prepared with a coating of silver salts. The vellum was then united with the original drawing, exposed to ultraviolet light, and later washed in a sodium thiosulfate bath. In an archival setting, Van Dyke prints are relatively rare, as they were created for temporary purposes and often discarded after the final positive prints were made. Because of the nitrates used in preparing the paper and the preferred thin paper itself, Van Dyke prints are often extremely brittle and susceptible to damage. Van Dyke prints should be stored separately and, when possible reformatted before the image degrades unacceptably.