Skeletons of various prehistoric beasts were among the many specimens displayed in Planet Ice: Mysteries of the Ice Ages, our recently ended special exhibit that will soon launch its tour across Canada and the US. While some were actual fossilized specimens from our collections, others were reproductions or what we call “casts.” On the road, the real fossils that were available for viewing in Ottawa will also be replaced by replicas. 

Two fossil skulls on display in a museum.
Two fossil specimens—a 13,000-year-old beluga whale (Delphinapterus leucas) skull from Ontario (top) and a cave bear (Ursus spelaeus) skull from Europe (bottom)—as displayed in Planet Ice: Mysteries of the Ice Ages. Having premiered in Ottawa, the exhibit will move on first to the Ontario Science Centre in Toronto; however, these two specimens will be replaced by replicas and the original fossils returned to secure storage at the Canadian Museum of Nature’s research and collections facility in Gatineau. Catalogue numbers: CMNFV 21336 (beluga), CMNFV 7760 (cave bear). Image: Scott Rufolo, © Canadian Museum of Nature (beluga); Martin Lipman, © Canadian Museum of Nature (cave bear) 

The safety of our specimens is always our main concern when determining what to display in an exhibit, especially if the exhibit is destined to travel. Fossils are extremely fragile and essentially irreplaceable; each one is unique and offers a distinct window into the past. It is often my job to fabricate a reproduction when it is considered too risky for one to be on tour. 

When necessary, we make every effort to create accurate replicas to provide visitors with an educational and engaging display. Highly detailed resin replicas are made either by creating casts from molds taken from the original specimens, or through 3-D printing in combination with the use of 3-D imaging technology. Either way, these casts are usually a solid colour (typically white) and still require painting in order to match as closely as possible the appearance of the original specimen. 

Museum visitors frequently ask: “Are all fossils brown?” In short, no, but I find the long answer much more interesting. Once an animal—dinosaur, mammal, or otherwise—has died, there is a particular set of circumstances that needs to happen for fossilization to occur. If these essential requirements are met and the animal’s remains are covered quickly enough, then the fossilization process can start. 

Dinosaur skeletons on display in a museum.
Dinosaur skeletons in the Canadian Museum of Nature’s Fossil Gallery. Approximately 80 per cent of the specimens on display are real fossils. Out of that number, around 90 per cent are brown. Most of the dinosaur material is from Canada, where the fossils formed through permineralization in iron-rich environments. Over thousands of years and under extreme pressure from the weight of accumulating layers of sediment, the bones become encased at the microscopic level in iron-containing minerals that imparted a dark, reddish-brown colour. Image: © Canadian Museum of Nature 

However, there are several possible pathways to fossilization involving different types of minerals. It is the specific minerals that largely determine the final colour of each fossil. Minerals around the world vary greatly in their physical properties: structure, hardness, and lustre, to name a few. The sediments and ground water immediately surrounding the animal where it was buried generally contain minerals in a range of colours. 

As the minerals in the surrounding material penetrate a buried bone, eventually coating—and in some cases replacing—the original organic content, the now fossilized bone takes on the physical properties of these minerals, including colour. Such colours are generally not bright blues, reds, or yellows, but range from pitch black to snow white, dusty rose to pale yellow, light beige to dark drown. 

In North America, many fossils contain phosphate, limestone, or iron. Phosphate typically produces black fossils and limestone yellowish-gray fossils. However, many of them, especially those of dinosaurs, are found in iron-rich areas, which generally produces the various shades of reddish-brown fossils that can be seen at the museum.

Five skeletons of extinct mammals on display in a museum.
Mounted replicas of the skeletons of various Ice Age mammals included in the Planet Ice exhibit. The giant beaver (Castoroides ohioensis) on the far left sticks out for its pale appearance in comparison with the darker colouration of its companions. Its reproduction is based on a specimen from Minnesota that was preserved in an environment containing light-toned minerals. Catalogue number: CMNFV 44757 (beaver). Image: Martin Lipman, © Canadian Museum of Nature 

The colour of a fossil reflects the environment in which the animal was originally buried, slowly fossilized, and eventually found. The colour may be able to tell us what the area was like when the animal died, geologic events that have happened since then, and where to look for similar fossils in the years to come. Therefore, when painting the replicas, it is extremely important to accurately reproduce the colour of the original fossils in order to fully convey their story of life, death, and discovery. 

Four photos of a replica whale skull, demonstrating the different stages of it being painted.
Successive stages in the painting of the beluga skull replica to be included in the travelling Planet Ice exhibit. A. The initial, unpainted 3-D print (the skull is upside down in this photo compared to the others in the series); B. Following preparation with a primer and base coat to establish foundations of the general colour; C. Greater details of colour variation and surface features added; and D. Final version, with fine details of tone, gradations, and surface variation added.  Image: Alan McDonald, © Canadian Museum of Nature 
Photograph of a replica whale skull next to the real fossil on which it is based.
The final, fully detailed replica next to the original fossil for comparison. Can you guess which is which? The real skull is on the right. Image: Alan McDonald, © Canadian Museum of Nature