Plaster of Paris.
Strips of thick cardboard or plastic
A Mixing bowl
A notebook and pencil
A camera and /or video camera.
A ruler or tape measure, or other scale indicator.
One of the biggest difficulties is in preparing the correct consistency of Plaster of Paris so that there are no air bubbles and fine detail can be seen. The plaster should be of the consistency of condensed milk. Always add the plaster to water and prepare enough to cover the highest part of the track by about 15 milimetres.
Although snow can give the best tracks, because the plaster of Paris gives out heat as it sets, good casts are impossible to obtain. Sand and soft silt also pose problems. In these cases, good clear photographs are the best method of identification.
Once the plaster has set, most of the soil can be removed, but detailed cleaning should be left until the cast is taken home, when it will be completely set. Newspaper makes a good transport wrapping. Casts can be cleaned with a soft brush and the details may be coloured. They should be clearly labelled with the location, date and a grid reference in possible.
Rather than taking a cast (which is fiddly and time consuming) it is very simple just to lay a sheet of acetate over a track and trace the outline, this will provide a lot of information and detail if done reasonably carefully. Detailed analysis of such data has regularly been used for differentiating dog from cougar tracks in cougar surveys in the USA.
I've just been reading the instructions by Chris on how to make a plaster cast and would like to suggest the following idea which I frequently used when carrying out examinations at crime scenes.
Probably the cast that gives the most problem is the one left in snow. As Chris rightly states the plaster of Paris gives out heat as it sets often distorting the shape. My advice is to photograph or sketch the track first then immediately before pouring in the plaster, give the print a light spray of hair spray. In this way I was able to make perfect casts which stood up to the ultimate tests in the Criminal Courts.
Practice makes perfect.
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