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.
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.
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.
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.
Canadian Museum of Nature Blog 
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