A cast of
a Grallator Track from the Triasssic Period some
200 millions years ago.
Scientists often are able to identify a known
animal, or be alerted to a new species by examining the tracks
left by the animal in the soft mud or soil after a rain. Scientists
have two techniques that allow them to make a permanent record
of these tracks for further study: photography and casting.
Photographing tracks is quick and easy, but doesn't
capture the track in three dimensions. Casting, by pouring a
liquid into the track and letting it harden, creates a copy
of the paw, claw or flipper that originally made the track.
Traditionally plaster of Paris has been used to fill the track,
but any substance that will fill out the impression and then
harden to maintain the shape will do.
Once the cast is made it, in turn, can be used
to create a cast of the track and that in turn can be used as
a mold to make additional casts of the animal's foot. In this
manner many scientists can study the track while only one of
them needed to make a trip into the field to discover it.
Casting isn't only done with recent tracks in
mud. Tracks left by dinosaurs millions of years ago in what,
eventually, became hard rock, can also be copied by the casting
Casts aren't limited to tracks either. All kinds
of objects, including dinosaur bones and teeth, may be copied
by covering the object with a substance like plaster, letting
it harden, then cutting the cast in two. This forms a mold,
shaped like the object. By filling that with something like
liquid plastic, an exact copy of the shape of the object can
be made. Museums often use this technique to copy dinosaur bones.
This allows a museum that doesn't own an exhibit, say like a
Tyrannosaurus Rex skeleton, to get a replica of the skeleton
from casts made at a museum that does have the Rex bones.
of a Tyrannosaurus tooth made from a cast.
Copyright Lee Krystek 1996.
All Rights Reserved.