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DISCUSSION

Both methods (acrylic or Butvar) are useful in a controlled laboratory setting. However, use of spray acrylic in the field except under very calm wind conditions is problematic. Wind tends to disperse the acrylic more than Butvar sprayed with an airbrush. In addition, the use of the cellulose acetate and Butvar (both mobilized by acetone) aids in the formation of a firmer bond between the consolidated surface and the cellulose acetate. We only used cellulose diacetate, but other forms of cellulose acetate (cellulose triacetate, cellulose acetate butyrate and others) likely can be substituted, but are not as readily available. This method also provides semi-permanent preservation. However, molds should be stored at low temperature and humidity away from other chemicals in order to lengthen the life of the mold. This method can be done solely with Butvar, using many spray applications. However, the cellulose acetate provides significant support and tear resistance. Both the cellulose acetate and Butvar can be removed with acetone, thereby returning to the original unconsolidated sediment.

The final result of this method is a lightweight three-dimensional “peel” of the sediment surface with the underlying sediment (with grain size and sorting) preserved (fig.2). This method requires relatively little preparation of materials (no plaster mixing or retaining walls needed). While plaster will crush and distort during its application and latex tends to shrink (Goodwin and Chaney, 1994), the final result of the cellulose acetate application undergoes little, if any distortion or shrinkage. We have been unable to measure any shrinkage in the preserved structures. The collected surface can be trimmed with scissors or a knife to remove any excess, and particular regions can be excised, in order to be studied in greater detail. Even the individual sediment grains of a section can be removed and cleaned completely with application of acetone. Details of environmental conditions, including location, wind speed, and temperature, can be written onto the collected surface. All of the materials are readily available at art stores, plastic suppliers (acetate sheeting ~500m2 for ~$100), and other paleontological supply companies. The airbrush’s cost is approximately $2. The cellulose acetate is not toxic and does not pose a health risk. Acetone is highly flammable and should be used (even with Butvar) in a well-ventilated area away from open flames. The method is useful on a variety of substrates from clay to coarse sand, and it is quick (taking as little as 10 minutes in dry calm conditions), cheap (under $10 per application), and easy to do.

 

 

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