Architectural reprography

Last updated November 10, 2024

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 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.^[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.

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.^[3] 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.^[3] 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.^[3] 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.^[1]

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.^[1] 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.^[1] Van Dyke prints should be stored separately and, when possible reformatted before the image degrades unacceptably.

Diazotypes

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.

As with other earlier reprographic processes, a translucent original drawing was placed over a sheet of the sensitized paper and exposed to light. However, the next step exposed the paper to an ammonia gas. 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. Typically these prints have blue or dark purple lines on a mottled cream-colored background, although line and ground colors can vary.

A related process is the sepia Diazo print, which produced either a positive or negative print in dark brown and light tones. 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. In the negative printing process, additional resins and oils were sometimes added to the paper support to increase translucency. Positive sepia prints, generally made on opaque paper, were typically used as an alternative to positive blueline Diazo prints.

Both blueline and sepia prints were often poorly and cheaply processed, resulting in undesirable residual chemical content. Off-gassing of sulfurous compounds, image fading, and yellowing of the paper support are common signs of degradation and are not reversible. Diazo prints are also highly light-sensitive and can fade to illegibility within a short period of exposure to ultraviolet light.

In archival practice, Diazo prints are the most common reprographic format encountered in late 20th-century architectural collections. However, their inherent fragility and fugitive images, as compared with blueprints and earlier processes, makes their care problematic. Diazos—particularly sepia prints, which readily transfer color to adjacent papers—should be physically segregated from all other types of media. Exposure to light and pollutants in air should be minimized, and wherever possible, original drawings or reformatted prints should be kept for reference.

Other processes

Hectographic prints
Ferrogallic prints
Gel-lithographs
Photostatic prints
Wash-Off prints
Silver halide prints
Electrostatic prints

Cleaning, flattening, and repairing

For large collections of architectural materials, conservation work can address several areas of concern. Consultation with a professional conservator is recommended, although some minor treatments can be accomplished by general caretakers with training. Rolled and folded reprography, once cleaned, can be flattened through humidification. Cleaning may be done with white vinyl erasers, using great care in areas of friable media, such as graphite and colored pencil. Tears, losses, and other surface damage should be treated by a professional conservator. For particularly fragile or frequently-handled prints, sheets may be encapsulated in polyester or polypropylene film for additional support and protection. This is not recommended, however, for reprographic prints with annotations in friable media.

Storage

Rolled storage

The most common form of storage for architectural drawings—both for drawings in active professional use and in archival environments—has traditionally been in rolls. While this allows for efficiency in the use of space and ease of retrieval, potentially damaging situations can arise from a casual approach to roll storage. For reprographic drawings on paper supports, rolling can stress paper fibers and make unrolling for examination more difficult. Small rolls can be easily crushed and ends can be creased and torn without additional protective wrapping and support.

Flat storage

In circumstances where fragile, rigid, or otherwise atypical media makes rolled storage unfeasible, storage in flat boxes or flatfile drawers can be the best choice. Acid-free and lignin-free portfolio boxes, ideally no more than four inches deep, can be cost-effective and allow more flexibility in arrangement on shelving. 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.

Drawings should be grouped and identified for ease in retrieval, preferably within folders that are cut to fit the full dimensions of the corresponding container. As with rolled materials, the potentially damaging chemical interactions of print processes should be considered when grouping drawings in folders. Wherever possible, for example, blueprints should be segregated from diazotypes, and sepia diazo prints should be stored alone to the extent possible.

Reformatting

For most drawings, especially those that are oversized or significantly damaged, photographic reproduction remains the best method of accurately reproducing the fine details of a drawing. For drawings that are not significantly damaged or that are encapsulated in a polyester film, digital flat-bed scanning or other mechanical methods may be used.

Professional resources

The Society of American Archivists supports many architectural archivists in their professional responsibilities. In particular, the SAA's Architectural Records Roundtable is a primary forum for discussion of issues of acquisition, identification, description, conservation, and digital preservation of a wide variety of architectural documentation.

Related Research Articles

A photograph is an image created by light falling on a photosensitive surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are now created using a smartphone or camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of what the human eye would see. The process and practice of creating such images is called photography.

<span class="mw-page-title-main">Blueprint</span> Document reproduction by contact printing on light-sensitive sheets

A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets introduced by Sir John Herschel in 1842. The process allowed rapid and accurate production of an unlimited number of copies. It was widely used for over a century for the reproduction of specification drawings used in construction and industry. Blueprints were characterized by white lines on a blue background, a negative of the original. Color or shades of grey could not be reproduced.

Reprography is the reproduction of graphics through mechanical or electrical means, such as photography or xerography. Reprography is commonly used in catalogs and archives, as well as in the architectural, engineering, and construction industries.

<span class="mw-page-title-main">Photographic paper</span> Light-sensitive paper used to make photographic prints

Photographic paper is a paper coated with a light-sensitive chemical, used for making photographic prints. When photographic paper is exposed to light, it captures a latent image that is then developed to form a visible image; with most papers the image density from exposure can be sufficient to not require further development, aside from fixing and clearing, though latent exposure is also usually present. The light-sensitive layer of the paper is called the emulsion, and functions similarly to photographic film. The most common chemistry used is gelatin silver, but other alternatives have also been used.

The cyanotype is a slow-reacting, photographic printing formulation sensitive to a limited near ultraviolet and blue light spectrum, the range 300 nm to 400 nm known as UVA radiation. It produces a monochrome, blue coloured print on a range of supports, often used for art, and for reprography in the form of blueprints. For any purpose, the process usually uses two chemicals: ferric ammonium citrate or ferric ammonium oxalate, and potassium ferricyanide, and only water to develop and fix. Announced in 1842, it is still in use.

Whiteprint describes a document reproduction produced by using the diazo chemical process. It is also known as the blue-line process since the result is blue lines on a white background. It is a contact printing process that accurately reproduces the original in size, but cannot reproduce continuous tones or colors. The light sensitivity of the chemicals used was known in the 1890s and several related printing processes were patented at that time. Whiteprinting replaced the blueprint process for reproducing architectural and engineering drawings because the process was simpler and involved fewer toxic chemicals. A blue-line print is not permanent and will fade if exposed to light for weeks or months, but a drawing print that lasts only a few months is sufficient for many purposes.

Ozalid is a registered trademark of a type of paper used for "test prints" in the monochrome classic offset process. The word "Ozalid" is an anagram of "diazol", the name of the substance that the company "Ozalid" used in the fabrication of this type of paper.

Sun printing may refer to various printing techniques which use sunlight as a developing or fixative agent.

A microform is a scaled-down reproduction of a document, typically either photographic film or paper, made for the purposes of transmission, storage, reading, and printing. Microform images are commonly reduced to about 4% or 1⁄25 of the original document size. For special purposes, greater optical reductions may be used.

Hand-colouring refers to any method of manually adding colour to a monochrome photograph, generally either to heighten the realism of the image or for artistic purposes. Hand-colouring is also known as hand painting or overpainting.

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<span class="mw-page-title-main">Tracing paper</span> Paper made to have low opacity, allowing light to pass through

Tracing paper is paper made to have low opacity, allowing light to pass through. Its origins date back to at least the 1300s where it was used by artists of the Italian Renaissance. In the 1880s, tracing paper was produced en masse, used by architects, design engineers, and artists. Tracing paper was key in creating drawings that could be copied precisely using the diazo copy process. It then found many other uses. The original use for drawing and tracing was largely superseded by technologies that do not require diazo copying or manual copying of drawings.

From the late 19th century until the middle of the 20th century, drafting linen, also known as drafting cloth, was commonly used as an alternative to wood-pulp and rag papers in creating technical drawings. Its major benefits were considerable strength, especially in erasing and redrawing, durability in handling, and translucency for making multiple reprographic prints. Manufactured as an undyed muslin woven fabric, typically using cotton or linen fiber, the textile was highly starched and then calendered to create a smooth surface for precise ink and graphite lines. Although drafting linen was most typically used in creating original drawings, it was occasionally used as the underlying support for blueprints and other similar reprographic processes. Drafting linen largely fell out of favor after the development of drafting film — varying in chemical composition from cellulose acetate to polyester—in the 1950s.

Screenless lithography is a reprographic technique for halftoning dating to 1855, when the French chemist and civil engineer Alphonse Poitevin discovered the light–sensitive properties of bichromated gelatin and invented both the photolithography and collotype processes. After the invention of the halftone screen in the 1880s, screenless lithography was abandoned. Until the end of World War II, two kinds of photomechanically made plates were used in lithography: albumin plates and deep-etch plates. Presensitized plates appeared in the 1950s, and wipe–on plates appeared in the 1960s.

Vesicular film, almost universally known as Kalvar, is a type of photographic film that is sensitive only to ultraviolet light and developed simply by heating the exposed film.

A heliographic copier or heliographic duplicator is an apparatus used in the world of reprography for making contact prints on paper from original drawings made with that purpose on tracing paper, parchment paper or any other transparent or translucent material using different procedures. In general terms some type of heliographic copier is used for making: Hectographic prints, Ferrogallic prints, Gel-lithographs or Silver halide prints. All of them, until a certain size, can be achieved using a contact printer with an appropriate lamp but for big engineering and architectural plans, the heliographic copiers used with the cyanotype and the diazotype technologies, are of the roller type, which makes them completely different from contact printers.

A contact copier is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface. The more common processes are negative, where clear areas in the original produce an opaque or hardened photosensitive surface, but positive processes are available. The light source is usually an actinic bulb internal or external to the device

The conservation and restoration of woodblock prints, is the process of caring for and repairing images made from a specific printing process involving using wooden reliefs to stamp or imprint an image onto paper. The process of creating woodblock prints as Asian examples are known, or woodcuts as Western examples are called, has been known for many centuries, and many older prints have experienced aging and deterioration of the paper and colorants used.

IBM manufactured and sold microfilm products from 1963 till 1969. It is an example of IBM attempting to enter an established market on the basis of a significant technical breakthrough.

References

1 2 3 4 "Architectural Drawing Reproduction". Preservation Self-Assessment Program (PSAP), University of Illinois. Retrieved 2024-11-03.
↑ Olcott Price, Lois (1995). "THE HISTORY AND IDENTIFICATION OF PHOTO-REPRODUCTIVE PROCESSES USED FOR ARCHITECTURAL DRAWINGS PRIOR TO 1930" (PDF). Topics in Photographic Preservation. 6: 43.
1 2 3 Olcott Price 1995, p. 44.