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How are fossil replicas made?

Making a Fossil Replica
The first phase in making many replicas is constructing a mold.
The first phase in making many replicas is constructing a mold.
© 2008 HowStuffWorks

A good fossil replica has to be detailed enough to show all the features of the original. But it can't be made of delicate material -- it has to be strong enough to support its own weight and withstand environmental stresses. Today, there are lots of different methods and materials used to achieve these two goals.

One of the most common methods of making a fossil replica is the mold and cast method. Typically, this process follows the same basic steps. The person making the fossil:

  1. Makes a clay base to support the fossil
  2. Paints the exposed side of the fossil with a flexible material, such as liquid rubber or dental molding, after coating the fossil with a release agent -- like diluted detergent -- if necessary, to safely free the fossil from the mold material
  3. Reinforces the flexible material with something sturdier, like fiberglass sheets
  4. Removes the finished mold and repeats the process for the other side

These steps may be impractical for the bones of an enormous dinosaur like Argentinosaurus. To make the replica of the dinosaur housed at Fernbank Museum of Natural History, sculptors created an artificial skeleton out of foam and clay and used it as the basis for the mold [source: Boyle]. A similar process can also allow researchers to recreate bones that are missing or damaged from the original skeleton.

The second phase is using the mold to make a cast.
The second phase is using the mold to make a cast.
© 2008 HowStuffWorks

The next major step is to make a cast of the mold. Typically, this involves filling the mold with a resin or plastic. Once the cast has hardened, artists can dye or paint it to match the original fossil. Museum staff can assemble these casts using steel supports called armatures to create a skeleton for display.

The mold-and-cast method is common, but it isn't practical for all types of fossils. The mummified hadrosaur known as Leonardo, for instance, is one solid piece rather than a collection of separate bones. To make a replica of Leonardo, Ford Motor Company used rapid prototyping. The first step was to use computed tomography (CT) scans to create a 3-D map of Leonardo's body. The next was to use stereolithography and selective laser sintering to produce a physical reproduction of that map. Both of these technologies use lasers to solidify a liquid or powdered substance, creating a model [source: Ford]. Researchers have used similar technologies, sometimes relying on laser scans or other measurements to create the original map. For large dinosaurs, it can take weeks to perform all the scans, resulting in enormous data files used to create the reproduction.

Right now, paleontologists can use materials like dental molding to create fossil molds in the field. Increasingly portable technology will also make it easier for researchers to collect the data needed to make a reproduction without ever leaving the dig site. But amateur reproduction of fossils in the field is another story. Even an experienced researcher can damage a fossil when trying to make a reproduction. In certain cases, like creating casts of dinosaur tracks, some damage is inevitable. Plaster and other casting materials can also permanently stain fossils, so it's a good idea to let the experts handle the molding and casting.

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