Architectural reprography

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.

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.

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.

[1] 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.

[2] 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.

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.

By the middle of the 20th century, wet-process reprographic techniques such as blueprinting, Pellet, and Van Dyke printing were largely superseded by various dry-printing processes.

The most common of these is the Diazotype process, refined in the 1920s, which used paper supports sensitized with diazonium salts, a coupling agent, and an acid stabilizer to produce a dark line on a white ground.

The Diazo positive print was considered more readable than a negative blueprint, and the dry process eliminated the image distortion of wet paper.

This alkaline gas catalyzed a reaction between the diazo salts and the coupling agent to produce an image that fixed in the paper over several days.

The negative versions of these prints were most often produced as intermediaries, like the earlier Van Dyke process, to allow corrections and revisions without disturbing the original drawing.

Flatfile furniture should meet the minimum requirements of archivally-sound construction—powder- or enamel-coated steel units with no rust or sharp edges that could damage materials while stored or moved in and out of the drawers.