Paper

For generating records of enduring value, adhere to ANSI (American National Standards Institute) Standard Z39.48-1992. These papers will:

• have a pH between 7.5 and 10
• be made from cellulose fibers (cotton or 100% chemically purified wood pulp)
• contain no more than 1% lignin (as indicated by a Kappa number not greater than 7)
• contain a minimum alkaline earth salt reserve equivalent to 2% calcium carbonate based on dry weight of the entire paper.

Specifications for enclosure formats, papers, plastics, adhesives, and printing inks are outlined in ISO (International Organization for Standardization) 18902:2001.

All enclosures need to be chemically stable and pose no physical harm when in contact with archives materials.  Paper enclosures, cartons, and boxes adhering to this standard will:

• have a pH between 7.0 and 9.5
• be made from high alpha cellulose, bleached sulfite, or bleached kraft pulp with an alpha-cellulose content greater than 87%
• contain an alkali reserve equivalent to 2% calcium carbonate, evenly distributed
• contain less than 0.0008% reducible sulfur

be free of:

• highly lignified fibers (groundwood)
• knots, shives, or other abrasive particles
• waxes, plasticizers
• alum rosin sizing
• metal particles

Enclosures that pass the Photographic Activity Test (PAT), ISO 14523:1999 [formerly ANSI IT9.16-1993] will not adversely react with photographic images.

In general, paper storage enclosures should be alkaline (pH not less than 7.5). Even materials such as blueprints, cyanotypes, color photographs, or albumen prints, considered "alkaline sensitive" may be safely housed in alkaline enclosures so long as they do not come into direct contact with moisture or high relative humidity (above 60%). Alkaline enclosures will last longer than their neutral counterpoints and uniform enclosure specifications for papers and photographs will help minimize staff confusion. If moisture is of great concern, you may wish to use enclosures in which pH neutral materials (pH not to exceed pH 8.0) are in direct contact with objects.

Neutral pH (7) paper housing materials are recommended for natural science specimens and ethnographic proteinaceous collection materials (e.g., leather, skins, fur, feathers, birds, mammals, silk, and wool.)

Plastics

• inert or chemically stable
• naturally flexible: no added plasticizers; internally plasticized
• dimensionally stable: will not shrink, expand, or distort under normal conditions.
• adequate strength
• clear; no coloring dyes; not frosted (frosted contain silica dioxide)
• smooth
• no added ingredients (UV inhibitors/anti-block agents/slip-agents, additives/coatings)
• flexibility of film matched to need

Request Material Safety Data Sheets (MSDS) to be assured of the absence of undesirable components in plastics to be procured.

Commonly Used Plastics in Archives Preservation

• Polyester film (polyethylene terepthalate): (1960s) DuPont Mylar Type D, ICI Mellinex 516. Though stable, it has a high static charge, a sharp edge, and because of its smoothness, can cause ferrotypying if used with photographic materials in a high relative humidity environment.
• Polyethylene: (1942) For use in storage, seek high density polyethylene (hdpe) which avoids slip agents, but is translucent rather than transparent.
• Polypropylene: (1957) For use in storage, seek biaxially oriented polypropylene because it does not include slip agents.
• Acrylic: (1936) Rigid material used for exhibition cases and glazes for framing.

Considerations when using plastics

• Static charge: Plastics generate a static charge making them unsuitable for loosely bonded media (e.g., soft pencil, unfixed pastels and charcoals, flaking media or emulsions).
• Density: Plastics are dense and will result in accumulated weight.
• Trap moisture: Can cause ferrotyping (i.e., sticking, causing photo to become shiny)
• Limit air flow: Problem for cyanotypes.
• Tendency for plastics to slide over one another in unrestrained storage.
• Use for physical support: Because plastic enclosures can accelerate the deterioration of acidic items, include an alkaline sheet of paper (as a buffer) which may help slow down deterioration if plastic is being used to provide physical support.