Published online by Cambridge University Press: 20 May 2016
Macro- and microfossils are commonly preserved as external molds as a result of decay or dissolution of soft and mineralized body parts after compaction and cementation of the surrounding matrix. The molds, which often preserve external features of the organism in great detail, are difficult to compare to other specimens. To enhance study, positive casts are typically made. Numerous compounds can serve as a casting medium (Rigby and Clark, 1965; Rixon, 1976). In microfossil studies latex rubber (Klapper in Winder, 1966; Ellison, 1987; Tull et al., 1988) and silicone rubber (G. Miller, personal commun.) are the most commonly used materials. An alternative technique is to photograph the mold directly using a scanning electron microscope (SEM).