Time Capsules
Introduction
Containers filled many years ago with documents and other
artifacts are occasionally recovered from the foundations
of buildings. The material in these time capsules is often
in fragile condition and must be extracted with great care.
More frequently, time capsules containing current material
are put in place during construction of new buildings. Few
guidelines on this practice are available and much harm can
come to enclosed material prepared improperly and buried under
inadequate conditions. The following information is intended
for people who have retrieved old time capsules or who are
intending to bury new ones.
Old Time Capsules
Copper sheet and tinplate were the most commonly used materials
of the 19th-century time capsule maker. They were most often formed
into boxes or tubes and were sealed with a soft, lead/tin solder.
In general, time capsules made this way survive in relatively sound
condition. However, moisture trapped in the interior, together with
caustic flux used in soldering, may cause significant corrosion
of both the copper and the underlying steel of the tinplate. This
results in a highly acidic environment, which causes discolouration
and possible disintegration of the enclosed materials, especially
if they are organic materials like paper, leather, and textile.
Also, if different metals are kept in contact for long periods of
time, small electric cells are set up in the presence of moisture
and salts. Corrosion at the joins of containers is accelerated under
these conditions. This can happen between the constituent metals
of the solders and the materials that they join.
Occasionally, bottles have been used to enclose documents and other
materials. A well-sealed bottle made of stable glass may survive
very well, but there have been instances of glass containers being
broken due to foundations shifting, frost creeping, or carelessness
at the time of retrieval.
The material of which the container is made is not the only factor
that may affect the contents. Once a time capsule is sealed, the
micro-climate within will dictate the fate of its contents. Obviously,
if water vapour and oxygen are trapped inside, they will interact
with any susceptible materials and will cause degradation. While
the container itself may not corrode, metal artifacts inside will
be affected by the presence of water and oxygen. The by-products
of their corrosion will affect other materials with which they are
in contact. As mentioned above, organic materials like leather,
paper, and cloth may be stained by corrosion products or may disintegrate
altogether. Oxygen and water will also have a direct effect on organic
materials, causing chemical breakdown of their structures.
Some materials, particularly mass-produced paper, are acidic by
nature, and sealing them into a closed environment will prevent
escape of their volatile acidic emissions. Acidic vapours can therefore
build up to levels far in excess of those normally encountered in
an open environment. Degradation is greatly accelerated under these
conditions.
Although they are not encountered very often in 19th-century time
capsules, relatively modern materials like rubbers and plastics
have been found to liberate acidic vapours. Similarly, paints, varnishes,
and other coatings on artifacts can contain synthetic materials
that are prone to degradation. The volatile by-products accumulate
within the enclosed space with a resulting increase in the rate
of deterioration.
Micro-organisms and fungus can also be sealed into a container
and, under the right conditions, can cause accelerated decay of
organic materials. Insects that feed on organic material (book lice,
for example) could be hidden in folds of paper or textile. Mould
spores, normally present on many materials, need only the right
environment to proliferate. All these biological agents will remain
viable as long as the supply of oxygen lasts.
Opening Time Capsules
Opening time capsules gives practical information on the relative
merits of containers and the durability of contents. It can tell
us a great deal about the right way to prolong, as much as possible,
the survival of the material within. The problems encountered when
attempting to open old containers indicate that the foresightedness
of our ancestors was concentrated primarily upon the contents.
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A time capsule that has been carefully retrieved
from a site should be handled with care; contents that havelain
undisturbed for decades may be in very fragile condition. Avoid
the very common practice of shaking the container, and keep the
orientation of the capsule as it was when found. This way, fragile
contents will not be disturbed, and any leaked water will not wet
previously dry materials. Examine the outside of metal capsules
very carefully for possible leaks in the seams or closures. Check
for inscriptions, which may include instructions for opening. There
is no simple way of determining the exact nature of the contents
of metal boxes without opening them; x-rays that are powerful enough
to penetrate the metal will show no shadow of less dense contents,
except perhaps solid metal objects like coins.
Opening a sealed metal box entails a certain amount of destruction.
Naturally, the cutting should be done as carefully as possible because
the box itself is a historical artifact, but one should not be too
concerned about causing damage; the container was made to be opened.
If a time capsule in a glass bottle has to be opened, cutting or
breaking the glass will obviously be a last resort, especially as
old glass bottles can be very valuable. There is nothing to be gained
by hurrying the opening. Material that has lain buried for decades
can afford to wait a few hours more.
In order to get an idea of the distribution of the contents within
the container, rest it on a 1/4" (6.3 mm) dowel and determine
its point of balance (see Figure 1). Assuming that the contents
are distributed evenly, this may give an indication of which end
is empty. Obviously, the presence of heavy artifacts like coins,
or perhaps leaked water, at one end could be deceiving.
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Open the time capsule on a stable bench or table covered with a
sheet of polyethylene. Do not attempt to reverse solder joins by
heating; it takes much less heat to make a solder join than it does
to open one, so damage to the contents of the capsule could result
very easily. Place the capsule on a pad of foam plastic, towelling,
or other soft resilient material so that it overhangs the edge of
the bench slightly. Wood blocks on two sides will be sufficient
to prevent the time capsule from moving during opening (see Figure
2). Before beginning with cutting tools, first drill a pilot hole
near one corner of the container. Surround a 3/8" (9.5 mm)
diameter drill bit nearly to the tip with a piece of 3/8" (9.5
mm) bore metal tubing (see Figure 3a). This provides a stop for
the drill to prevent its breaking through too far into the container.
If drill grinding equipment is available, the cutting angle of the
drill can be adjusted from the usual 60° to 30°, further
limiting penetration (see Figure 3b). Use a variable speed power
drill to drive the bit. Once the hole has been made, the interior
of the capsule can be inspected and the line of the cut can be plotted.
If possible, insert a fibre optic viewer through the hole to get
an idea of the disposition of the contents.
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Use a junior hacksaw with a fine-toothed blade
to cut open the capsule. This takes longer than using a large hacksaw
but allows for much better control. Stop cutting frequently to assess
progress and to check that none of the material in the interior
is being touched by the saw. It is often possible to insert a thin
ribbon of plastic through the drill hole to protect documents or
other fragile materials that lie close to the saw cut (see Figure
4). Square boxes only need to be cut on three sides; bend back the
fourth side to expose the contents. Circular containers, on the
other hand, must be cut almost all the way around. Before removing
the contents, turn back the edge of the cut with pliers to avoid
snagging on the contents as they are extracted.
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Once the contents are exposed, they can be carefully removed and
spread out on clean blotting paper. Separate artifacts from each
other, but do not attempt initially to unroll, unwrap, or unfold
papers. Paper and textile artifacts can be extremely fragile after
prolonged aging. Take special care not to stress the folds until
their exact condition can be assessed. All material removed from
the time capsule must be allowed to equilibrate to the ambient relative
humidity for several hours at least.
Unless the contents are judged to be in excellent condition, it
is advisable to contact a conservator for advice on care, handling,
and treatment.
Constructing a Time Capsule
By far the best modern material for burial is stainless steel.
It is relatively inexpensive and easily fabricated, and its stability
in adverse conditions is excellent. A container with a threaded
end cap and an O-ring seal will be easy to open (see Figure 5);
however, such a container is extremely expensive to make and the
materials in the O-ring might degrade over a long period of time.
As a less expensive alternative, use wing nuts to clamp the lid
in place (see Figure 6). Both of these designs have the disadvantage
that screw threads can become "seized" when left in contact
and under pressure for long periods, thus making them difficult
to unscrew. Another less expensive option is to make the box of
sheet metal and to weld it shut once it has been filled (see Figure
7). This will be more difficult to open but has the advantage of
excellent sealing, provided that the welding is done well.
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It is tempting to consider sealable plastic containers for making
time capsules, but too little is known of the long-term stability
of most plastics under burial conditions to warrant the risk. The
chances of the plastic cracking under cold conditions are very high,
and the seals would be suspect over a period of many years. Nevertheless,
it is possible to construct a "box-within-a-box" by encasing
a sealed plastic container in a thick layer of paraffin wax. Lay
the time capsule on a bed of wax 1" (2.5 cm) thick in the bottom
of a larger container, and pour melted wax all around and over the
top to a thickness of 1" (2.5 cm). On the other hand, sealable
polyethylene containers are quite adequate on their own for time
capsules intended for indoor use.
The Contents
A brief survey of the contents of time capsules opened by CCI staff
over a period of some years reveals a not-altogether-surprising
lack of imagination. In many cases, the capsules contain documents
of purely parochial interest, albeit of a timely nature. These may
include such items as newspapers of the day, parish registers, and
even annual church accounts. Documents of this kind found in time
capsules less than 100 years old may well be duplicated in local
archives, often in better condition than those enclosed in a capsule.
For example, in 90% of cases, a newspaper of the week or day of
burial is included in the capsule despite the fact that many newspaper
publishers have supported, and continue to support, substantial
archives of their publications. Similarly, circulated coins of marginal
numismatic value are often included. While these may provide a "touchstone"
to the past, they provide very little else, and certainly nothing
of specific historical value. Even though it is rare for the contents
of a time capsule to contain anything of more than local value or
interest, there are occasional dramatic exceptions.
With this in mind, it should be the prime responsibility
of the buriers to choose materials intelligently and to ensure that
the artifacts so chosen are appropriate and evocative of our times.
For example, consider including manufactured products of some complexity;
artifacts which, if they survive into the next century at all, will
not normally do so in unused condition, i.e., electronic calculators,
small power tools, wrist watches, etc. Another aspect of our throw-away
society is packaging material, some of which is very skilfully designed
and says much about our attitudes. If coins are to be included,
ensure that they have never been circulated or handled. A little
imagination will provide material of this kind that also has a local
interest.
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If possible, avoid paper documents, particularly
photographs unless they are of archival quality, due to their
known instability. If paper is included, separate items from
each other by enclosing them in sealed Mylar sleeves. A better
alternative to paper documents and photographs is archival-standard
microfiche. This is a great deal more stable and, of course,
much more economical of space. Avoid including magnetically
recorded material like audio or video tapes; unless these
are re-wound periodically, their quality can deteriorate very
badly. Also, it is not certain that such recordings will be
playable in the future, unless the retrievers have access
to working museum pieces! Compact discs can be included if
a player is also part of the inventory.
Conditioning the Interior
If the contents of the sealed container are to be preserved, it
is necessary to exclude oxygen and water as much as possible. (Light
must also be excluded, but this is not, of course, a consideration.)
However, it has been shown that a complete absence of oxygen can
cause certain mineral oxide pigments to fade. Also, it has been
reported that if materials such as paper and textile are completely
dried, they become brittle and can be severely damaged by careless
handling on retrieval. If a dry environment can be achieved in the
container, a warning on the fragility of the contents could be included
along with instructions for reconditioning them to ambient relative
humidity. For the ideal interior environment, therefore, aim for
a dry and relatively oxygen-free atmosphere. Several methods for
doing this are outlined below.
Passive Protection
If the capsule is sealed when the relative humidity is very low
and the air is cold, it is possible that the contents will be minimally
damaged during burial. This depends largely upon what the contents
are, the average temperature of the place where they will lie, how
much moisture they contain, whether they have corrosive components,
and whether they have a guaranteed long-term stability. In other
words, passive methods of protecting the contents (which one normally
encounters in early time capsules) are unreliable at best.
Drying
Drying is the single most important factor for the preservation
of materials. One of the most effective substances for absorbing
water is silica gel, which is used for conditioning the interiors
of packing cases, scientific instruments, etc. In order to make
the interior of a time capsule as dry as possible, at least one-fifth
of its volume should be packed with dried silica gel crystals, i.e.,
with silica gel that has been heated at 150°C in an oven overnight
to drive off all moisture. Indicating silica gel contains a dye
that will turn deep blue once it is dry. Spread the silica gel on
a metal tray to a depth of not more than 0.4" (1 cm) during
drying. Insert it into the time capsule after the contents have
been added and just prior to closing. The silica gel must be isolated
from the artifacts by placing it in a linen or cotton bag (see Figure
7). As an alternative to silica gel, a thick, multi-layered sandwich
of good-quality acid-free blotting paper may be used. The paper
should be dried in an oven in the same way as the silica gel before
being inserted.
Removing Oxygen
Even with all water removed from the interior of
the container, degradation of the contents of a time capsule can
still take place due to the presence of oxygen. Oxygen can be removed
by both passive and active methods. The capsule can be flushed with
dry nitrogen just prior to closing in order to displace most of
the oxygen contained in the air. Attach the lid of the container
and leave a small hole in which a hose may be loosely inserted.
The hose should reach the bottom of the container (see Figure 8).
Flush dry nitrogen from a tank through the capsule for at least
15 minutes, and then seal the hole quickly. This process is never
100% efficient; some residual oxygen will remain, which can be advantageous
if sensitive pigments are present.
Active removal of oxygen will occur when the oxidative degradation
of organic materials and the respiration of micro-organisms and
fungus take place. Thus, if the container is perfectly sealed, the
oxygen will be depleted to the point where the reactions cease.
Because oxygen constitutes 20% of the volume of the atmosphere,
removing the oxygen in a sealed container will result in a negative
pressure. Any slight leak in the capsule will allow air, water,
and debris to be drawn into the interior. Perfect sealing and a
strong container are critical in this case.
Preparing the Contents
Each artifact chosen for inclusion in the time capsule should be
enclosed in a polyethylene or Mylar bag, or in a box to ensure that
dissimilar materials are isolated from one another. For most stable
materials, it is better not to seal bags or boxes because the objects
only need to be isolated from each other, not from the environment
of the capsule. (Paper, and any other objects suspected of instability,
are exceptions.) Sealable plastic containers are very useful for
isolating materials from each other.
If paper documents are included, do not fold them sharply because
this stresses the paper and can cause fractures at the crease lines.
Folds can be padded with a stable polyethylene foam or with acid-free
tissue paper. Documents should be clean and free from any form of
contamination. Bulky paper works should be pre-dried for a few days
in a closed container with dry silica gel prior to their inclusion
in the capsule. (As mentioned previously, microfiche is a sensible
alternative.)
Metal objects should be free of visible corrosion and in sound
physical condition. Avoid polishing them before insertion unless
removal of polish residues can be completely assured. Resist the
temptation to apply protective coatings; there is no clear understanding
of their long-term effectiveness, especially in such closed environments.
Degrease metals with acetone to remove finger marks, which can cause
etching and corrosion, and make sure thereafter to handle the objects
with clean cotton gloves.
If an electronic device is chosen for inclusion, remove and discard
batteries. In their place, include a note stating the voltage and
current requirements of the device. Solar-powered instruments are
an attractive alternative. Individual components can be wrapped
in acid-free tissue paper before being put in polyethylene bags.
Also, package boxes and instruction manuals separately.
Sealing
With the methods of construction shown in Figures 5 and 6, it is
simply necessary to screw the lid firmly onto the container, thus
squeezing the O-ring and effecting an excellent seal. As an added
precaution, the ring and its seating can be coated with a silicone
grease (e.g., Dow Corning High Vacuum Grease) or the whole container
can be set in melted wax.
The welded box construction shown in Figure 7 requires more time
and care to seal completely but has a far superior seal. As can
be seen in the diagram, the lip to be welded is as far from the
contents as possible and is isolated from them by a layer of glass
fibre insulation. To avoid over-heating the metal, use an electric
arc, not a gas flame, for the welding. Check very carefully that
the weld is intact around the entire circumference of the lip.
If a welded box has been used, it is important to mark the end
that should be opened. The metal container can be indelibly marked
on the outside with a punch before it is filled. Similarly, a warning
may be placed on the box concerning the fragility of the contents.
Enclosing or Burying
It is not uncommon to find old time capsules buried below ground
level in the foundations of buildings. If the capsule is completely
sealed and has been prepared as suggested above, this generally
results in no damage to the contents. In fact, the container may
be better insulated below ground level than above. However, in less-than-ideal
interments, fluctuating temperature and ground water levels on the
outside may influence the interior, especially if significant amounts
of water remain inside the capsule. Condensation of atmospheric
moisture in the interior is a possibility under these circumstances.
Also, if stainless steel has not been used, corrosion of the capsule
will result. It is therefore best to enclose the time capsule in
a wall above the frost and ground water level.
Build a drained concrete or brick vault lined with fibreglass insulation
to minimize temperature fluctuations and to prevent water from getting
in (see Figure 9 ). If stainless steel has not been used for the
container, seal the container tightly in a polyethylene bag or enclose
it in a block of wax before cementing it in place. When the capsule
is cemented or bricked in, avoid resting any weight on it. Over
a long period of time, the seams of the box could become strained
and begin to leak. The site of the time capsule is often marked
on the outside wall with a plaque or carved inscription.
Conclusion
CCI staff have responded to many enquiries about construction and
preparation of time capsules. These enquiries have had one thing
in common: that the time capsule must be ready for burial in an
unrealistically short period of time. The planners rarely leave
enough time to do the job well. If a time capsule is to be buried
properly the correct materials must be used, the artifacts must
be selected and prepared with care, and the container must be made
to withstand its journey through time. It is a waste of effort to
prepare a time capsule in a hurry. There is nothing quite so sad
as a time capsule whose contents have deteriorated so badly as to
be useless.
There is absolutely no evidence to suggest that people 100 years
hence will have the slightest interest in time capsules. In fact,
considering the number of things piling up in museums, the many
fold increase in historical studies and books, and even the proliferation
of antique, junk, and collectible stores, it is more probable that
people of the future will be so inundated with historical material
that a time capsule may be less exciting to them than we anticipate.
Think about this and try to make the contents worthy of the effort
and evocative of the times we live in. Finally, if none of the above
advice is taken, at least ensure that a microfiche copy of this
publication is included so that our well-meaning intentions will
be properly construed.
Recommended Reading
Australian Institute for the Conservation of Cultural Material
(Inc.), The Preparation of Time Capsules. Information Sheet No.
3, Canberra: AICCM, 1992.
Durrans, B., "Posterity and Paradox: Some Uses of Time Capsules,"
in Sandra Wallman (ed.), Contemporary Futures: Perspectives from
Social Anthropology (Association of Social Anthropologists Monographs,
30), London and New York: Routledge, 1992.
Field, B.P., "U.S. History in a Box," National Geographic,
vol. 175, no. 5 (May 1989), pp. 652-660.
Fraser, Helen, The Time Capsule: Repository of the Past or Romantic
Notion? AASLH Technical Leaflet #182. Nashville: American Association
for State and Local History, 1992.
Jarvis, W.E., "Time Capsules," Encyclopedia of Library
and Information Science, New York: Marcel and Dekker, 1988,
vol. 43, supp. 8, pp. 331-355.
Logan, J.A. and G.S. Young, "'A Message in a Bottle': The
Conservation of a Waterlogged Parchment Document," Journal
of the International Institute for Conservation — Canadian
Group, vol. 12 (1987), pp. 28-36.
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