Fossil preparation

Fieldwork, involving targeting potential fossil-bearing rocks, then prospecting for, excavating, and collecting fossils (remains or traces of ancient life–including bones, teeth, shells, leaf, impressions, nests, and footprints–that are usually buried in rocks), is what most people think of when they hear the word paleontology (the study of ancient life). Popular culture references to expeditionary work and paleontological excavation make it seem exciting and glamorous. It certainly can be thrilling to discover a fossil that has been buried for millions of years, but even if you manage to find a fossil (and they are very rare) excavation is painstaking and physically demanding work.

In the mid-19th century, collectors in the American West would normally gather fossil fragments that were visible on the ground’s surface. The collector would dismount from his horse, look for additional pieces, place them in his saddlebag, and ship them back East with minimal packaging. When they arrived, hundreds of small fragments with little or no accompanying information would have to be laboriously pieced together.

By the early 20th century field techniques had improved. John Bell Hatcher was one of the first paleontologists to develop a systematic collecting process, which recorded the type, position, and orientation of fossils in the field. With the expansion of railroads in the American West, collectors were no longer as reliant on pack animals or wagons for transporting specimens.

The emphasis on field records has steadily increased in importance since Hatcher’s time. For paleontologists, fossil collection often is as much about collecting data as it is about collecting specimens, so the information associated with the specimen can be as significant as the actual fossil.

These data also are vital to the work of the preparator; they can provide information that helps to locate parts of the fossil that are buried deep in the rock and help to reassemble fragmentary specimens. Whenever feasible, involving a trained preparator in the excavation process helps ensure that the steps carried out in the field, such as jacketing the specimen, are done in a way that will assist the work back in the lab.

Fossils do not come out of the ground ready to use. Usually they are brought back to the institution in a field jacket, still embedded in matrix, and require preparation, the process by which the fossil is exposed, to enable them to be studied.

The extent to which a specimen gets prepared is determined by the paleontologist’s goals for that particular specimen and is usually undertaken with a specific aim in mind. They may be research goals e.g., to expose features for identification or for further study. Alternatively, the specimen might be prepared for exhibition; depending on the nature of the fossil, this could involve leaving the specimen partially embedded in matrix, or completely removing the matrix and mounting the fossil on a supporting armature.

Mechanical - using various types of physical force to remove the matrix from around the specimen.  Mechanical preparation utilizes tools that apply external physical force to sediment (also called matrix) in order to remove it from fossil bone. Tools used for preparation range from steel and carbide needles to mini-jackhammers and micro-sandblasters. While it is possible to use chemical and even some non-invasive techniques to reveal the specimen, mechanical methods are the most commonly used. Once the jacket has been opened, or if the specimen is not jacketed (as is often the case with small specimens), you will probably be faced with bone that is surrounded by rock. Before the specimen can be used for research or exhibit some or all of this rock must be removed to reveal the bone.

Chemical - applying particular compounds, or combinations of compounds, to the specimen to dissolve the surrounding matrix. While mechanical preparation uses physical forces to remove the matrix from around a specimen, in chemical preparation various compounds are used to dissolve the surrounding matrix. Just as a preparator must choose the right hand tool for mechanical preparation, picking the right technique for chemical prep is critical. Any preparation method can be damaging if done improperly, but acid prep can be particularly damaging because the chemicals can attack the fossil as well as the matrix. For this reason, chemical preparation should only be chosen if it will produce a superior result or if it is the only option to safely reveal the specimen.

Non-invasive – non-contact, non-destructive technological tools that can be used to obtain information from the specimen. Many of the tools and techniques used by today’s preparators have changed little since the origins of the field over 100 years ago.

However, in recent years a number of new technologies that have been applied to preparation are opening up exciting possibilities for paleontological research and preparation.

Three tools of particular utility are:

The use of these technologies is unlikely to replace traditional preparation methods anytime soon, but for some research projects and for certain specimens they can provide information that would be otherwise unobtainable.

Once preparation is complete, the specimen is almost ready to be used. Museums may use some specimens for display but generally only a small fraction of the specimens in a collection are used this way.

Most are intended for scientific research and are available for in-house or visiting scholars to study, or for loan to other institutions. Before this can occur, however, there are several activities that must take place.

Labeling: If a specimen becomes detached from its identifying number, it loses most of its scientific significance. The catalog number forms the link between the specimen, its associated data, and any derivatives such as molds, casts, and photographs or illustrations. It’s important that specimens and all their derivatives be labeled with the relevant catalog number, to avoid breaking this link.

Molding & casting: Another way to study the specimen and obtain additional information is by producing a cast. Casts are reproductions of the object, made by pouring a liquid material, such as plaster or a resin, into a mold which has been made from the surface of the specimen. While not an inherently destructive process, molding can be damaging if not done properly. It can also be very time intensive and, for large fossils, expensive.

Exhibition: Specimens intended for exhibit are often prepared differently than they would be for research purposes. The most complete specimens are often desired for both activities, which can lead to conflicting demands.

Housing: Specimens need to be housed and stored properly to ensure their long-term preservation. Factors such as the specimen’s size and type of preparation will affect what solutions are adopted.

Conserving: Although fossil specimens may seem strong, after all they have lasted millions of years, they are often extremely fragile. Preparation can make a specimen more vulnerable to damage, or may enhance its stability. Additionally, the use of adhesives, consolidants and other chemicals also has an effect on the long-term preservation of specimens.