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
- 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.
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.
Conservation & Preparation— working towards common goals
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. For more information on how conservation is relevant to fossil preparation download these presentations:
Applying a Conservation Model to the Treatment of Fragile Dinosaur Bone. A poster presented by 2005 L. Kronthal, Christina Bisulca, and Amy Davidson, at the 2005 Society for the Preservation of Natural History Collections Meeting. London, England.
- Basic principles of conservation and their application to paleontological collections: Preparation and collection care with purpose, a PowerPoint by Gregory Brown, University of Nebraska State Museum, Lincoln, NE presented at the 2007 SVP annual meeting.
- Preparation of a Fossil Dinosaur a pdf of a presentation given by Amy Davidson at the 2003 American Institute for Conservation Objects Specialty Group annual meeting (AIC Objects Specialty Group Postprints, Vol.10pp. 29-60).
- A Technique To Create Form-Fitted, Padded Plaster Jackets For Conserving Vertebrate Fossil Specimens a 2005 SVP Preparators Session paper by Jabo, S.J.; Kroehler, P.A.; Grady, F.V., Department of Paleobiology, Smithsonian Institution.
Read another example in A Mammoth of a Project: The Conservation of a Columbian Mammoth, a Masters thesis by Shanna Larea Daniel
Useful conservation resources
- Horie, C.V. 1987. Materials for conservation: organic consolidants, adhesives and coatings. London: Butterworth Heinemann.
- The Getty offers: AATA Online, A major database of conservation literature abstracts offered free by the GCI, in association with the International Institute for the Conservation of Historic and Artistic Works.
- The Conservation Information Network (CIN) provides: BCIN, the Bibliographic Database of the Conservation Information Network, is the Web's most complete bibliographic resource for the conservation, preservation and restoration of cultural property.
- JAIC Online, The Journal of the American Institute for Conservation is a major source for conservation literature.
- Information on materials can be obtained from CAMEO a searchable information center developed by the Museum of Fine Arts, Boston. The database contains chemical, physical, visual, and analytical information on over 10,000 historic and contemporary materials used in the production and conservation of artistic, architectural, archaeological, and anthropological materials.
- Shelton, Sally Y. 1994. Conservation of vertebrate paleontology collections. Vertebrate paleontological techniques Volume 1. Patrick Leiggi and Peter May eds. New York: Cambridge University Press.
- Shelton, Sally Y. and Dan S. Chaney. 1994. An evaluation of adhesives and consolidants recommended for fossil vertebrates. Vertebrate paleontological techniques Volume 1. Patrick Leiggi and Peter May eds.New York: Cambridge University Press.