How to Make Casts of Real Dinosaur Tracks
When dinosaur tracks are discovered in rock, it is best to leave them in
place so they can be studied the way they were formed millions of years ago.
Often someone wants to study a footprint, but cannot stay at the tracksite, or
people want to learn about the track but it is located in a dangerous, dedicate,
or difficult to reach place. In these cases, a replica of the dinosaur track is
made. If you are able to visit a place where real dinosaur tracks are located,
then you may be allowed to make your own cast of the track to have as a
permanent souvenir.
1.
Preparation: It is important to get permission from the landowner before
making casts of any dinosaur track to avoid doing damage to a fragile fossil.
Choose a track made in relatively level rock to prevent loss of plaster during
molding. The track should be cleaned out by sweeping dust and other dirt before
beginning the cast process. The dry surface of the track and surrounding rock
must be lightly coated with petroleum jelly, cooking oil, liquid soap, or
another nonstick material to prevent the cast medium from becoming stuck to the
rock.
Next,
build a retaining wall or cardboard or posterboard or springform pan side
surrounded by rags on the outside around the track to capture wayward plaster.
The wall should surround the track a few inches away, be a few inches high, and
also be coated with nonstick material. The wall can be sealed and secured to the
rock using clay or modeling clay if there are large gaps.
2.
Cast Batter: Plaster of paris is the cast maker of choice because it is
inexpensive and easy to use. As a guide, a foot-long track may engulf up to 10
pounds of plaster. Mix the plaster powder with fresh water using a ratio of two
parts plaster to one part water until it is lump-free and resembles thick cream
or cake batter in consistency Add a few drops of liquid detergent to discourage
bubbles and enhance the smoothness. The next steps must be performed immediately
so the plaster does not begin to set before it is poured.
3.
Making the Cast: When casting a very large track, reinforce the cast with
wire mesh, fabric such as cheesecloth, or even clean twigs placed in the middle
of the plaster. Pour the plaster batter slowly and carefully into the prepared
track, attempting to keep bubbles at a minimum, and filling all crevasses. While
the plaster surface is still wet, use wet hands or trowel to smooth the top.
Once the top begins to harden, it can be marked with the location, date, and
caster (even a child's handprint). Let the plaster set for at least an hour, the
longer the better. The process is faster when the weather is warm and dry.
4.
Unveiling the Cast: Remove the retaining wall, rags, and attached clay. Lift
the cast out of the track in a smooth motion. Be sure to record the details of
the track: location, type of dinosaur, date of cast, and castmaker.
A lightweight, durable, but more expensive alternative to plaster of paris is
latex (liquid rubber). Track preparation is simpler, involving only the sweeping
out of the track. The latex may need thinning with water, then it is applied
directly to the track using a paintbrush or fingers. The first, very thin coat
should dry some, but not completely, in a few hours. Then the second coat should
be added. A reinforcing layer of cloth can be placed between the layers
Another interesting option for trackway casting is to use the dental casting
material, Alginate, available from local or mail order dental supply companies.
Alginate is supplied as a powder, in a choice of flavors! It is inexpensive,
priced around $3 per pound, and very fast and easy to use. Equal amounts of
water and powder, measured by volume, are squeezed together in a plastic freezer
bag for one minute or less. The white paste is poured or squirted from a small
hole in the plastic bag directly onto the track surface. Within a few minutes,
the Alginate dries to a flexible solid which may be removed from the track. The
final cast is durable, but can be torn or cut.
A mail order supplier of Alginate:
Towne International, Inc. (Dental Supply)
717 E. Ordnance Rd., Suite 206 Baltimore, MD 21226 (401) 766-5261
http://www.townedent.com
