What is a Time Capsule?
Contrary to popular imagination, time capsules do not have to be buried. A good time capsule -- one that successfully preserves its contents before it is next opened after a planned period of time -- requires only:
- A good storage container
- A good place to keep the storage container
- Careful consideration of what to include in the container
In other words, storage considerations for a good time capsule are not very different from those for good storage in general. The main point of distinction is that general storage takes into consideration regular or occasional access to the contents, whereas a time capsule is intended to stay closed and undisturbed until it is opened after a certain period of time. The objective in both situations, however, is the same: that the contents remain in as good a state of preservation as possible.
Choosing a Good Storage Container
- Choose a tightly closed container that will keep out light, dust and other air-borne pollutants, and water
- The container material should be chemically inert, e.g.: uncoated polyethylene (PET or PETE, recycle code 1) jar with a screw-top lid of the same material; uncoated high-density polyethylene (HDPE, code 2) or polypropylene (PP, code 5); aluminum or stainless steel cans with matching screw-top lid; lignin- and acid-free cardstock boxes with snug lids (will keep out minimal, incidental water only)
Choosing a Good Location for the Container
- A cool (room temperature or below), relatively dry (about 35% relative humidity), clean, and stable environment (avoid attics, basements, and other locations with high risk of leaks and environmental extremes)
- Minimal exposure to all kinds of light; no exposure to direct or intense light
- Distance from radiators and vents
Content Considerations
Even with a good storage container and location, which certainly help to minimize the chemical processes that result in deterioration, materials will still decay if they are inherently unstable. Furthermore, deterioration of one material in the time capsule can lead to deterioration of the other materials contained in the time capsule, since they are in a limited, closed space together. Well-preserved time capsules require careful consideration of what materials are included. Some considerations:
- Analog items are not machine-dependent, but digital items are; include the machine required for digital items and instructions for use
- Materials that have already withstood the test of time have proven to be long lasting; the long-term behavior of new materials is more unknown
- Safer, more traditional choices include: items printed or written with carbon-based ink on acid- and lignin-free, good quality paper; well-processed black-and-white photographs; non-corroding metals; textiles made of non-plastic fibers; glass; stone; ceramic; items made of uncoated PET, HDPE, or PP plastics
- Further minimize the risk of unexpected chemical interactions among the time capsule contents by packaging each item: put each item or group of like items in acid- and lignin-free paper envelopes, folders, or boxes; uncoated PET zipper bags; or glass or PET, HDPE, or PP plastic vials with screw-top lids
- Avoid including food items and plants or other living things
- Include a list of the contents in the time capsule and why they were included
- Minimize the risk of mechanical damage: put heaviest items at the bottom; prevent items from rattling around; ensure the weight of the contents within the time capsule container is evenly distributed; indicate on the outside of the container which side is up
The above guidelines are intended as a basic starting point. Institutional time capsules require more stringent precautions.
Resources
- Gerald R. Ford Conservation Center, Nebraska State Historical Society, Time Capsules and Preservation [PDF: 189 KB, 5 p]
- Iowa State University Library, So you want to do a time capsule? [PDF: 55 KB, 2 p]
- Minnesota Historical Society, Time Capsules
- National Archives of Australia, Creating a time capsule
- New York Times Magazine, Built to Last – a Dialog With Experts on Building Time Capsules , December 1999
- New York Times Magazine, How to Make a Time Capsule , November 2015
- Smithsonian Institution, Time Capsules and Teaching with Time Capsules: Learn How to Select a Collection of Items to Include In Your Time Capsule (and What You Should Exclude!) [PDF: 70 KB, 3 p]
- Conservation Corner: Reminding the Future, Library of Congress Information Bulletin, on the Library's Bicentennial time capsule containing a collection of artifacts that capture the texture of life in 2000
