Conserving

Research associate Amy Davidson seated at a table wearing glasses and a head lamp, using tools on a fossil.

Amy Davidson, Research Associate, doing fossil prep.
© AMNH

Most museum fossil collections are full of examples of the various ways in which old preparation techniques have failed to withstand the test of time.

Discolored coatings, failed or sagging joins, flaking or powdery surfaces, acid attack, wire hanger armatures pulling apart fragments, etc. are all ways in which the materials and methods have adversely affected the long-term preservation.

Preparators often have to deal with these challenges when specimens are requested for research, loan or exhibition. In approaching a specimen that has already been prepared the preparator is acting in much the same way as an art conservator would. The situation must be assessed and then redressed.

The conservation model of approaching a specimen involves:

Scientific testing
Documentation
Preventive care

Some examples of ways in which preparators may have to conserve specimens include:

Documentation

One of the distinctions that separate an art conservator from a restorer is the commitment to documenting all materials and techniques used on a cultural object undergoing any form of preservation intervention. This documentation (both written and photographic) is vital, in the same way medical records are important for assessing the health and ongoing care for a human being. It provides:

Material evidence of pre-treatment conditions if and when needed.
A guide for future conservators that helps to inform their decisions (i.e. what might have worked or failed in the past).
A record of tests and investigations already carried out.
Information on ways intervention may modify analytical results.
A body of information for future surveys or similar activities.
Full documentation to be used for insurance purposes should a claim be necessary.

Preparation labs benefit from having a documentation policy and corresponding procedures to ensure that information is kept on the preparation and treatment materials and methods for all specimens.

Repairing failed or sagging joins

When joins in fossil specimens sag or break it may be necessary to repair them. As discussed in the section on adhesives and consolidants there are many options available. Some of these materials have been extensively researched by art conservators. Others that have not been found to be useful in conservation may not have much research or published literature but may still have a valid place in fossil preparation. It is important to choose the right material, based on an accurate understanding of its properties. Two general guidelines are:

Use an adhesive strong enough to do the job – but not too strong. If an adhesive is stronger than the fossil fragments being joined then future breaks will occur in the specimen rather than along the old break edges.
Know your glass transition temperature (Tg). Sagging or slumping joins occur when an adhesive’s Tg is exceeded. If fossil storage areas are not temperature controlled the Tg of some commonly used adhesives can easily be exceeded. This should be considered when choosing an adhesive for joining fragments. To learn more about Tg download the SPNHC wall chart table.

SPNHC Leaflets Adhesive and Consolidants Wall Chart

Removing coatings or joins

Fossils may be impregnated with consolidants (sometimes called hardeners by preparators) during field collecting; coatings applied years ago may have become tacky and dirty or may have yellowed and flaked over time. This is the reason why conservators generally try to choose treatments that are reversible. In conservation, reversibility means the ability to undo a treatment without incurring any damage or alteration in the original object. Reversibility is not always possible, but it is something that should be considered when choosing an adhesive or consolidant.

Will you have to remove the consolidant you used in the field once you begin preparation? Might you need to undo a join if an additional fragment is found? Is it possible that the coating will need to removed to prevent discoloration? These are all instances where considering reversibility may be important for preparators.

Transparent coatings

Transparent coatings can be made ‘visible’ using a black light (long-wave ultraviolet illumination). Coatings applied to the surface of a fossil specimen will fluoresce revealing their extent. With the exception of shellac, which glows a bright orange under UV light, the fluorescence is not diagnostic but it can be a useful tool when removal of a coating is necessary.

Conservation and Preparation: Working Toward Common Goals

“Paleontology is one of the last collection-based disciplines to adopt the principles of conservation science, perhaps because fossils were long deemed, somewhat naively, as being somehow invulnerable to the agents of deterioration that affect other collections. Today, preparators are keenly aware of the need to choose appropriate materials and techniques if we are to properly preserve the specimens and the data they contain, and are coming to understand that conservation principles lay at the very heart of our discipline. Incorporating these principles into our own practices, papers and presentations, and expecting them in others’, has become a hallmark of the modern preparator.” —Greg Brown, Methods in Fossil Preparation, Proceedings of the First Annual Fossil Preparation and Collections Symposium

Preparators must be able to understand the compromise between extracting the maximum amount of information from a specimen and preserving it for as long as possible.

Pyrite "Disease"

Pyrite (or iron persulfide: FeS2), also known as “fool’s gold,” is a common mineral that is often found in sedimentary rock. In some fossil deposits pyrite gets incorporated into bone, invertebrate shell, and plant fossils during the process of fossilization. If these fossils are exposed to conditions of high humidity, “pyrite disease” (also known as pyrite “rot” or “decay”) can occur.

The mineral oxidizes and forms iron sulphate (FeSO4); this oxidation product is several times the volume of the original mineral and the resulting crystal growth and expansion causes the specimen to fracture and crumble. The best way to combat this problem is by good “preventive conservation” focusing on keeping fossils in dry conditions—under 45% RH—is the only way to prevent this deterioration. Once the damage begins it is irreversible and specimens should then be kept in RH under 30%. While there are some remedial treatments, and more information can be obtained on these in the references below, good storage practices are the most efficient route for preservation.

These Fossil Preparation resources were originally developed in 2007 with the support of the National Science Foundation (NSF).