The Field Museum has three fossil preparation labs: two are located on the third floor; and one, the McDonald's Prep Lab, is located adjacent to Evolving Planet on the second floor. The McDonald's Prep Lab is fully viewable to the public. Research-based preparation is conducted in all three labs; and a team of skilled volunteers assist the staff preparators.
Fossil preparation is the removal of matrix to expose fossil specimens by mechanical, manual or chemical means.
Mechanical prep is performed with pneumatic tools: small jack-hammers of various sizes and sand-blasters, grinders and drills. This is usually done under a microscope, so the fossil will not be damaged by tool marks.
Manual prep involves the use of hand tools: sharp pin vises, dental tools, fine art brushes, etc. The matrix is removed carefully with the aid of a microscope, so as not to scratch fossil surfaces.
Chemical preparation is typically a series of immersions of a specimen into a weak acid bath. A specimen is partially embedded in a clear resin, unexposed side up. After removal of excess matrix by mechanical means, it is ready for its immersions. The acid dissolves the limestone matrix, and bone begins to appear. The specimen must be rinsed thoroughly, dried, and a thin coat of glue is applied with a small art brush to all exposed bone surfaces. The specimen is then ready for its next immersion. Again, a microscope is used for this delicate work.
There are other aspects to fossil preparation, too. Repairing and reconstructing specimens, micro-sorting (looking for tiny fossils), molding and casting, proper storage and labeling of specimens, tool and lab cleaning and maintenance, and keeping records (written and photographic) are all part of the weekly routine in the prep labs.