Time capsule - what to place in the cornerstone
Sealing a time capsule inside the cornerstone turns the ceremony into a message addressed to the people who will one day stand where the building now begins. The tube or casket placed in the foundation gathers documents, images and small objects that, together, describe a single moment in the life of an institution and the community around it.
Choosing well matters more than choosing much. A short, deliberate selection of items that survive decades intact says far more than a crowded box that decays in damp concrete. This guide explains what to include, what to leave out, and how to seal the capsule so it can be opened a century or more from now.
What a cornerstone time capsule is for
A cornerstone time capsule is a sealed container deposited in the foundations during the laying ceremony and intended to remain untouched until the building is rebuilt, extended or demolished, or until a chosen anniversary. It records who built the structure, when, and in what world they lived.
Treat the capsule as a curated archive rather than a souvenir drawer. Every item should answer a question a future reader might ask: who were these people, what did they value, and what did their everyday life look like? We help organisers plan, assemble and seal capsules as part of a complete ceremony, with services priced individually.
What to place inside the capsule
The core of any capsule is the foundation act itself, accompanied by material that puts the project in context. The list below covers the items that consistently earn their place.
- The signed foundation act (erection act), ideally on archival, acid-free paper
- A current newspaper or two, capturing the news, prices and tone of the day
- Coins and a banknote in circulation at the time of the ceremony
- Building plans, elevations or renderings printed on a durable, archival medium
- A list of participants, investors, architects and contractors with their roles
- A letter to the future from the founders or the community, kept short and personal
- A few small, flat mementoes: a stamp, a medal, a pin, a printed photograph
What to avoid placing inside
More capsules are ruined by the wrong contents than by a failed seal. Anything that can rot, rust, off-gas or release moisture will damage everything packed beside it, so a handful of categories should never go in.
- Perishables: food, seeds, plants, flowers or anything organic that decays
- Liquids and gels, including pens, scented items and sealed bottles
- Damp or freshly printed material that has not fully dried out
- Batteries, electronics and magnetic media that degrade or leak over time
- Ordinary photo paper or inkjet prints prone to fading; favour archival prints
- Rubber bands, low-grade plastics and adhesives that harden, melt or stain
How to seal a capsule to last 100+ years
Longevity comes from three things: a corrosion-resistant container, a genuinely hermetic closure and a dry interior. The container should be made of a metal that resists rust, such as stainless steel or copper, with walls thick enough to survive the pressure of surrounding concrete.
Close the capsule so it is airtight rather than merely capped. A welded or soldered seam, or a gasketed screw closure, keeps out the moisture and air that drive corrosion. Adding a sachet of desiccant inside controls residual humidity, and wrapping fragile documents in acid-free, inert material protects them from contact with the metal.
- Use stainless steel, copper or another corrosion-resistant metal
- Seal hermetically by welding, soldering or a gasketed closure
- Add desiccant to absorb any moisture trapped inside
- Line the interior and wrap documents in acid-free, archival materials
- Place the capsule in a dry recess and protect it from direct concrete contact
Planning the capsule alongside the ceremony
The capsule works best when its contents are decided early, well before the day of the ceremony, so documents can be printed on the right paper and the container prepared and tested. Items collected at the last minute are the ones most likely to fade or fail.
Decide too how the capsule will be recorded and, ideally, when it is meant to be reopened. A note in the building's archive describing the exact location and contents ensures that a future generation knows the capsule exists and can find it. We coordinate this planning with the wider ceremony; the service is priced individually.
Frequently asked questions
What should always go into a cornerstone time capsule?+
The signed foundation act is essential, ideally on archival paper. Beyond that, a current newspaper, coins in circulation, the building plans on a durable medium, a list of participants and a short letter to the future form a strong, lasting core.
What must never be placed inside?+
Avoid anything perishable or moisture-prone: food, seeds, flowers, liquids, batteries and cheap plastics. These decay, leak or off-gas and will damage the documents and keepsakes sealed alongside them.
What material should the capsule be made of?+
Choose a corrosion-resistant metal such as stainless steel or copper, with walls thick enough to withstand the surrounding concrete. The aim is a container that will not rust through over a century or more underground.
How do you seal a capsule so it lasts over 100 years?+
Make the closure genuinely hermetic by welding, soldering or using a gasketed screw seal, then add desiccant inside to control humidity. A dry, airtight interior is what protects the contents from corrosion and decay.
Can you help us prepare and seal the capsule?+
Yes. We help organisers select contents, source the right archival materials, prepare and seal the container, and coordinate the deposit during the ceremony. The service is priced individually to suit each project.
Planning a cornerstone laying ceremony?
Tell us about your investment - we will prepare a run-of-show and a quote tailored to your construction site.