Architectural Papers (Diazo)

Risks of Handling/Use

Generally, handling and use heightens the risk of damage to your materials, be it through neglectful handling (e.g. touching photo emulsion with bare hands) or irresponsible operation of access equipment. This is a risk posed by patrons and staff alike, intentional or not.

Handling and Collections Care

One of the easiest areas to implement protections for collections is through careful handling and sensible collections care. The unfettered use and handling of materials heightens the general risk of damage--be it through neglectful handling (e.g. touching photo emulsion with bare hands) or irresponsible operation of access equipment. Whether intentional or not, this is a risk posed by patrons and staff alike.

Examples of neglect, mishandling, and mismanagement include:

General Recommendations:

Additional Copies

The use of additional copies for reference or display purposes is highly recommended, particularly if the item is an original or valuable. This provides broader access to the content while also protecting the original document from user wear and tear or environmental factors.

Recommendations for care of original object:

To learn more about best practices for use and access, including resources for creating digital surrogates, see Use & Access in the User-Manual.

Orientation in Storage

Store flat. If space for flat storage is not available, it may be acceptable to store the prints rolled. Brittle or otherwise fragile prints should not be rolled. Prints that are strong and flexible enough to be rolled must have an interior support, which should be a neutral pH cardboard tube (over 3" diameter) wrapped in polyester or neutral paper. The rolled print and interior support may be wrapped in the neutral paper or polyester, and they should be stored horizontally, not upright. Prints should not be folded; this will create fold lines that stress the paper fibers and cause it to tear. All storage materials should pass the Photographic Activity Test (PAT) as specified in ISO Standard 18916:2007.

Storage Container

Technical prints were generally not made with long-term stability in mind; most were created quickly and cheaply to serve an ephemeral, utilitarian purpose. Many of these prints will retain chemical residues from processing. These residual chemicals may off-gas or cause damage if placed in contact with other prints.

Prints are usually large; they should be stored horizontally in flat files or rolled if flat storage is not possible. Enameled steel, stainless steel, or anodized aluminum flat files are preferred. Store different types of architectural prints separately in order to prevent contact degradation. Alkaline storage enclosures are not advised for ferro-gallic prints. Folders cut to drawer size are recommended, with less than 12 prints to a folder and with interleaving sheets placed between them (both neutral pH). Individual prints should be stored in polyester sleeves within folders in order to protect particularly fragile items and to separate formats from one another. Polyester sleeves also provide additional support during handling.


If your item has any kind of labeling on the container, the item itself, or any related material, we highly recommend that you return to the Basic Info section and enter this information in the appropriate field(s).

Labeling on a container or on the item itself, if it is in fact correct, can offer important clues about its content. If you are replacing a container that holds labeling information, it is important to transfer this information to the new container or label. Be sure to copy down any titles, dates, or other data found on these items and save your notes. Container labels should be used with caution as they are frequently reused or easily switched by accident.

For sleeves and folders especially, remember that it's generally best to label with a no. 2 pencil. If ink must be used (i.e. on a plastic enclosure), use an archival pigment-ink pen (e.g. Micron).

Physical Damage

Regardless of its acidity and inherent vice, all paper is susceptible to tearing and other forms of mechanical damage. Water exposure can affect the structural integrity of paper, leading to desiccated or brittle paper, which is more easily torn and damaged through handling. If paper has been folded, creased areas will be especially vulnerable to tearing.

Unbound paper may be damaged by fasteners like paper clips, and they are especially at risk during removal of fasteners. Metal fasteners that are not stainless steel will eventually corrode, and plastic fasteners may cause warping. For information on the correct removal of fasteners, consult the NEDCC leaflet on the Removal of Damaging Fasteners from Historic Documents.

Impact of Damage on Visual Information

Due to residual chemicals, paper will likely be brittle. Edges may also be discolored. Yellow and brown discoloration is more likely to occur on the image-side of the print and along the edges.

When evaluating the impact of damage on visual information, look for mechanical damage as well as deterioration and decay that obscures or limits access to information. This could include yellowing and embrittlement, both types of damage especially symptomatic of newsprint and other wood pulp papers. Damage could also include fading, darkening, warping, cockling, blocking (especially of coated papers), tearing, mold, and insect infestation.

Mold / Pest Damage

Pests like insects and rodents tend to like paper and textile materials. High humidity (higher than 68% RH) promotes mold growth and insect infestation, both of which can cause permanent damage. When assessing the exposure of your collections to pests, it is necessary to look not just at the materials themselves and their containers, but also to look at the larger environment. Insects and rodents tend to leave droppings in areas they inhabit. Insects tend to leave behind a substance called frass, which is the undigested fibers from paper. If you see droppings and/or frass in the storage area, it is a strong sign that your materials are being exposed to pests. Small, irregular holes on paper-based enclosures are also a sign that pests have attacked your materials.

Some tips for reducing your materials' exposure to pests are to refrain from eating anywhere near your collections materials. Crumbs draw pests, so keep food far away from your collections. Another tip applying to both pests and mold is to be cautious about donated materials when you receive them. Pests and mold can hitch a ride into your facility on these materials, so having a good, clean staging area where you can inspect donated items for, among other things, pest and mold evidence can help you reduce your storage environments' exposure to both.

Support Type

Diazo prints are most frequently found on paper supports, though they may also be on polyester or acetate film, or drafting cloth. Regardless of the support material, high temperatures and high humid environments should be avoided.

Drafting cloth support (and ground) may discolor or stain over time. Paper prints are at risk for yellowing and embrittlement. Like paper, prints on a plastic support may become brittle or yellowed, depending on the type of plastic.

For more information, visit the supplementary profile for Architectural Drawing Reproduction Support in the Collection ID Guide.

Paper Decay

Paper is sensitive to light and water exposure, high humidity, and high heat. Exposure to light and/or heat will accelerate deterioration in the form of yellowing and sometimes embrittlement.

Acidic paper (pH below 7.0) commonly exhibits both deteriorative traits. Colored media on the paper support will fade rapidly. Water exposure can ultimately lead to desiccated or brittle paper, making it more easily torn or damaged through handling. Fluctuating temperature and RH may result in warping or cockling of the paper surface. High humidity (higher than 68% RH) promotes mold growth and insect infestation, both of which can cause permanent damage.

Even pH neutral papers will become increasingly acidic over time. This is due to the fact that cellulose naturally generates acids as it ages. Papers, including book leaves, that are darker and more brittle along their edges than center demonstrate an absorption of airborne pollutants that have formed acids.

Soil and dust may become ground into paper fibers, permanently soiling or staining the paper surface. Foxing is a common form of paper deterioration, which manifests as reddish-brown spots or blotches that appear embedded in the paper surface. Foxing is caused by a number of factors, but it is commonly spurred along by high humidity.

Film Support

Plastic drafting film has been used since the 1940s, and it was the preferred support from the 1980s through the 2000s. Drafting films will have a matte finish on one or both sides, which gives the surface "teeth" to accept media (i.e. pencil, ink) or emulsion. Like other translucent supports, drafting film may be used alternately for original drawings or as a reproductive intermediate. Reproductions were likely run through a diazo machine. Stability will largely depend on composition.

Acetate (1939–present; significant decrease in 1960s)

Early acetates are especially prone to shrinking, and they may exhibit bubbling or "channeling" between layers due to disparate warping. Acetate with "vinegar syndrome" can infect other acetate-based materials stored nearby, particularly in a poorly ventilated storage area. Deterioration is hastened by high RH. Acetate film, if it is suffering from acetate decay, will emit an vinegar odor. Segregate acetate film in unbuffered paper sleeves. Do not enclose in polyester sleeves. Reformat if possible.

Polyester, or Mylar (c. 1950–present; popular after 1970)

Debuting in the 1950s, polyester became the standard film material in the 1970s. It cannot be easily torn and is considered chemically inert—despite some reported reaction to the diazo process. If stored in appropriate conditions, polyester may last over 500 years. Drafting film is commonly referred to by the trade name Mylar. Some early drafting polyester matte coatings (1950s–1970s) are known to flake; reformat these as soon as possible. Store all polyester film flat in acid-free folders. Interleaving with unbuffered paper may help prevent image transfer or loss.

If you are having difficulty identifying your the base material, see Film Base Materials in the Collection ID Guide.

Cloth Condition

Architectural reproductive prints are often found on drafting cloth supports, or prints on paper may be mounted on muslin cloth. Cloth supports may become limp due to the presence of residual and oftentimes acidic chemicals. Mechanical damage and deterioration may result in fraying.

Drafting cloth is among the most common supports found in 19th and early 20th century architectural and technical drawing collections. Introduced in the 1850s, this flexible, durable alternative to paper was used primarily by architects and engineers for process drawings, tracings, and reprographic prints (e.g. blueprints, diazotypes).

The fabric is typically cotton or linen, which is starched and calendered to create a smooth, glossy drawing surface. Over time, additional oil and plasticizer treatments improved translucency and water-resistance in drafting cloths. Prior to the 1880s, cloths had an off-white or natural color; after 1880, a bluish-white tint was common, due to a colorant used to increase transparency.

By the mid-20th century, drafting cloth fell out of favor after the emergence of synthetic (i.e. acetate and polyester) drafting film. Regardless of composition, some refer to all types of drafting cloth as drafting linen, or simply as "linen."

Ink/Media Deterioration

All diazo prints should be assumed fragile and volatile. Diazos were often poorly processed; and, as a result, they will contain residual chemicals harmful to themselves and other materials stored in proximity. They are also known to transfer color dyes to adjacent papers. Diazos should therefore be stored separately from other materials if possible. Original drawings or reformatted copies, if any, should be retained. Alkaline storage enclosures are not advised for diazo prints.

The azo dye-based image or text may be faded, particularly if either housed in an unsuitable enclosure (see Storage Container for more information on proper storage) or exposed to light for an extended period. Residual chemicals and light exposure can together cause yellowish-brown discoloration in unexposed areas. Diazos must be stored separately from most photographic materials due to their destructive off-gassing. Sepia diazo prints, frequently used as intermediate images, may be coated with wax, paraffin, or oil to increase translucency. This coating may transfer to other objects and results in a characteristic reddish pink discoloration or greasy smudging.

Characteristics of ink and other media vary depending on their composition and method of formulation. As such, the stability of media has a long-term effect on its paper support, and vice versa. It should be assumed that all media has potential to fade under extreme light exposure and that ink will bleed or transfer if exposed to moisture.

For assistance evaluating symptoms of media deterioration, see Common Types of Media.