Outdoors. Animal tracks may be found in mud or dust, or an animal may be induced to walk across a prepared strip of damp smooth earth (Figure 40).
To make a plaster cast of tracks in moist earth, make a circle of a 1 to 2-inch wide piece of celluloid, fastening it with a paper clip. Press this celluloid circle about 1/8 of an inch into the earth surrounding the track; this will retain the plaster and form the outer edge of the cast (Figure 41). Now mix the plaster and pour it into the mould, filling the mould to a depth of from 3/4 of an inch to an inch. Let the plaster harden, and when it is hard, remove the celluloid and lift the cast from the track. When it is fully dry, wash or wipe off any dirt that may have clung to the cast.
If the cast is made in soft dust, put on the celluloid ring, and with a fixative blowpipe (Figure 42) (used for fixing charcoal drawings) blow a fine watery spray of plaster of Paris over the dust, settling it and making it possible, when the spray has dried, to pour in the regular plaster mixture without destroying the track. Hold the ring down firmly so that the plaster will not seep out from under it while you are pouring.
Indoors. Tracks can be made by pressing the animal's foot into clay, plasticine or warm paraffin. Proceed as directed for tracks made in moist earth.
These casts, when complete, show the track in bas-relief, or humping up where the track made by the animal was sunken in. To give the track its natural appearance, grease the cast track surface and the sides of the cast with vaseline, lard or any other grease, first removing any particles of dirt. Fasten the celluloid around the cast again and pour on another layer of plaster. When it is hard, gently pry the two casts apart and you will have negative and positive casts of the track (Figure 43). Do not try to make a second cast of a track that has "undercuts" which would cause the two casts to be locked together.
An animal track cast, when made into a paperweight or wall plaque, is an interesting souvenir of a pet show, a day in the woods, or a memento of a favorite pet. A collection of track casts offers a way of studying animal adaptations and differences. How many toes has your cat "fore and aft? " Your dog? The chances are you'll have to look to be sure, and well as you thought you knew your pet, you probably guessed badly.
Casts of leaves, twigs, flowers, ferns, closed cones and nuts may be made very easily and do not require a second cast to give them a natural appearance (Figure 44).
Roll out plasticine or clay on a board or paper, spreading it out 1/4 to 1/2 inch thick. This can be done with a stick and the hands, or a glass or bottle may be used to roll it.
Moisten the glass with water if the rolled material tends to stick. Cones and nuts will naturally require thicker clay than flowers or ferns. When the clay is evenly spread, lay the flower or specimen on the clay and press it 1/8 or 1/16 of an inch into the clay, using the fingers or rolling the specimen with the glass.
Use the fingers to press a rolled specimen that is thin further into the clay, taking care to press it in evenly, avoiding oval finger impressions that will show up in the finished casts as bumps.
When a leaf is being cast, press the veined side into the cast. Remove the specimen and proceed as directed for animal tracks in clay. Casts of this kind are most effective if they are painted to resemble the natural color of the specimen and labeled properly. Collections of casts of leaves, twigs and flowers may be made in this fashion (Figure 45) and used as paper-weights, wall plaques and book ends.
A very quick, inexpensive, neat and orderly way of mounting a mineral collection is to mount the specimens in plaster bases (Figure 46). Make a ring, square, or the particular shape you desire of tin, celluloid or cardboard, lay it on a flat surface, and pour in plaster to the depth selected for the finished bases. Before the cast hardens imbed the mineral to be mounted in the plaster, being careful to arrange the specimen so that its best side protrudes. These casts, when dry, may be labeled or numbered. An individual cast for each specimen is better than imbedding a whole collection in one large cast, making a bulky collection that cannot be rearranged. If all the specimens are about the same size, the collection will be more attractive. Shellac the casts, for handling will soon make an unprotected cast very dirty.