In my job as a Web Content Developer at the Canadian Museum of Nature, I often get an inside look at the work my colleagues are doing. Recently, I happened across a set of photos showing one of our exhibition contractors casting a sedimentary rock face on a remote hill. When I learned more about the casting process and the exhibit, I was impressed and I thought that you may be interested too.
Our contractor, Research Casting International (RCI), is building us a new interactive exhibit. It’s a replica of a remarkable sedimentary rock deposit in Saskatchewan.
RCI’s technique and artistry are marvellous—it’s an utterly convincing reproduction. It looks so good that it’s even difficult to tell where the cast picked up bits of real rock from the mould.
The hard work started on a steep slope of a hill in Saskatchewan. Two days of digging 12 feet (3.5 m) into the hillside revealed the 7′ high × 16′ long (2.1 m × 4.9 m) face of sedimentary rock that would be replicated.
To make the mould for the cast, the RCI team first applied a skin of latex and coarse cloth to the entire surface of the rock face, taking great care to coat even the finest details. Next came a coat of a different latex to act as a shield between the first layer and the last. The final layer of fibreglass and polyester resin provided a sturdy cradle to support the latex/cloth layer, helping it keep its intricate three-dimensional shape. Thus the mould comprises two parts: the flexible latex layer and the fibreglass shell.
Back in the shop in Trenton, Ontario, RCI assembled the mould and laid it on the floor. They built a “bridge” on wheels to go over the mould so that the casting crew could access every part from above, usually while lying down. Two people worked on the bridge for about two days while four others mixed and coloured the casting material and otherwise supported the hands-on work.
The first layer of the cast is the surface that you will see in the gallery. It is a gel coat polyester resin that was tinted to match the real rock. The crew brushed each batch of coloured gel into the mould to match the varied colouration of the real rock face.
Once that was done, the crew built up a thicker layer on top out of fibreglass and polyester resin. That layer forms the back and supports the cast, which is like a wall in the gallery. RCI also incorporated steel fittings into that layer for attaching the wall to the custom steel frame that holds it up.
Once the frame was welded on, what remained to do in the shop was to peel off both parts of the mould, and then the wall was basically ready for installation in our new Earth Gallery.
After the wall arrived in the gallery, a museum palaeontologist, the exhibit content developer and the lead RCI creator consulted on the applied fossils. The fossils will serve as traces of events in Earth’s history to be discovered by visitors as they interact with the exhibit. All the fossils represent species that are appropriate to the time and place, and all are casts of real fossils—most of them from the museum’s collection.
As of this week, not much remains to do. Once the last couple of fossils are in place, RCI will apply a final coat over everything to seal and consolidate the surface. To finish, the museum team will complete and install the exhibit labels and guide for helping visitors explore the secrets that lie within.
And that’s the point of the exhibit: we’re inviting visitors to put on their pretend geologist’s hat and “read” the rock face to discover the stories that sedimentary rock records in its layers.
Knowing that the Earth is in constant change, I’m pretty amazed that any record of Earth’s billions of years is preserved so that we can find and interpret it.
Sedimentary rock is able to preserve traces of the environment (think fossils) and geological events (e.g., erosion, tectonic plate movement) because of the way it forms. Sedimentary rock is the result when particles from weathered and eroded rock accumulate in layers and then get compacted and cemented together. The traces are preserved when they get sandwiched in the layers and transformed into rock along with the sedimentary particles.
When the museum team was developing plans for the gallery, they knew they wanted to include something that would let visitors discover such traces—and the stories they embody—for themselves.
Once the team hit upon the idea of having a sedimentary rock face in the gallery, the decision to make it a Canadian example of an extraordinary formation known as the K-Pg boundary soon followed.
This formation is important because scientists were able to interpret the evidence it presents about Earth’s history and figure out that a giant meteorite strike was likely a main cause of the extinction of the dinosaurs.
The K-Pg boundary is a thin layer that settled across the world about 65.5 million years ago when the meteorite strike threw up vast amounts of debris and ash. Its line runs across the middle of the museum’s replica, a mere moment in the approximately six million years represented by the wall’s layers.
We hope that visitors to the gallery will enjoy spotting this trace and others in the wall and learning about what they mean—activities that are similar to what palaeontologists and geologists do.
So, on your next visit to the gallery, make sure to look for the large sedimentary rock face that’s quietly minding its own business in the back. Get close and look deeper, and perhaps once your visit is over, you’ll find yourself looking at the rocks around you with new understanding and interest in the history they record.
And of course, before “digging in”, I hope you’ll take a moment to admire the stunning realism of the replica rock face.
The new Earth Gallery opens at the Canadian Museum of Nature on November 30, 2012.