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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 have lain 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.
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.
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.
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.
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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.
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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.
