SECTION:   4 MUSEUMS IN ONE / NATURAL HISTORY RESEARCH

Natural History Research

Our Natural History collections include fossil, rock, mineral, entomology, osteology, malacology, herbarium, taxidermy, ornithology study skin, bird egg and nest, and alcohol-preserved collections of fish, reptiles, amphibians and invertebrates. If you would like to visit to study our research collections, need more information on a specimen, or would like to borrow a specimen, please contact the Registrar of Natural History:

Rodrigo Pellegrini, MA, MS.
Registrar, Natural History Bureau
New Jersey State Museum
PO Box 530
Trenton, NJ 08625-0530
USA
Voice: (609) 292-5615
Fax: (609) 292-7636
E-mail: Rodrigo.Pellegrini@sos.state.nj.us

USE OF BEESWAX AS A CONSOLIDANT IN
PYRITE-DISEASED FOSSILS

JEHLE, Albert. P. O. Box 544, Langhorne, PA 19047; GRANDSTAFF, Barbara Smith, University of Pennsylvania, Philadelphia, PA 19104-6316; and PARRIS, David C., New Jersey State Museum, P. O. Box 530, Trenton, NJ 08625-0530

ABSTRACT

Fossils containing iron sulfides sometimes deteriorate spontaneously.  This usually is a result of alteration of pyrite or marcasite to melanterite and other iron sulfates that occupy greater volumes than the parent mineral. The resulting expansion causes fractures. Sulfuric acid produced by the reaction discolors and damages fossils.  This process is known as "pyrite disease".

Using consolidants to seal a fossil's surface and deny atmospheric access can prevent conversion of marcasite/pyrite to melanterite. Some consolidants may become brittle when cured. Evaporation of volatile solvents can limit their depth of penetration. Sulfide minerals may exist below the consolidated zone. If a thin, brittle sealant layer cracks with time it will open routes by which atmospheric oxygen and water vapor can interact with sulfides to destroy the fossil. Beeswax is tough and resilient, and requires no volatile solvents. It penetrates deeply, permeating and fully encapsulating fossils and forming a barrier that is resistant to failure.

Beeswax treatment requires fossils and wax to be gradually heated to temperatures of 80-120oC. Heating drives off bound water, dehydrating the sulfate minerals that were produced by sulfide oxidation and decreasing the likelihood of further reactions. Sulfur and other residuals taken up by the wax can be removed from fossils by draining the wax. Heating also helps kill bacteria, which mediate some iron sulfide reactions.

Some disadvantages of beeswax as a consolidant include variability of composition, difficulty of removal, and incompatibility with other adhesives. However, for salvage of partially damaged specimens, it remains a safe and inexpensive method, requiring only simple apparatus.

INTRODUCTION

Iron sulfide deteriorations cause some of the most vexatious problems in museum conservation. So-called “pyrite disease” is so familiar that a historical review is scarcely necessary. From the Iguanodon assemblage of Bernissart (a priceless national treasure) to specimens in the most obscure private collections, almost every earth science curator in the world has had to deal with this problem. And while great museums may be able to devote considerable efforts to conservation, the average collection lacks the resources to deal with such matters. The specimens may never be treated, even if the problem is discovered while there is still time to act. Many venerable specimens of fossil vertebrates from New Jersey have been irretrievably damaged, often before the deterioration was noted.

The processes described here have considerable antiquity, but remain useful for many current situations. The methods are available to organizations with very limited resources, a significant advantage. Furthermore, the possibility of salvaging specimens of historical importance (despite the presence of major damage) requires careful consideration.

The New Jersey State Museum is experimenting with using beeswax to salvage fossils that are badly affected by pyritic deterioration. Fossils from glauconitic sediments in the New Jersey coastal plain contain microcrystalline pyrite, which is commonly associated with glauconite (Deer et al., 1966). Pyrite reacts with atmospheric oxygen and water vapor to produce iron sulfates. Sulfate product minerals have lower specific gravities than the sulfides they replace (Ford, 1932: Palachi et al., 1944-1954; Gaines et al., 1997) and occupy larger volumes. Mineral expansion causes fossils to crack. Sulfuric acid formed during sulfide oxidation may add to the damage. Microcrystalline sulfides also affect bones from Pleistocene bog deposits in New Jersey.  Minerals involved in "pyrite disease" are listed in Table 1.

TABLE 1: Minerals Involved in "Pyrite Disease"

Several methods of limiting pyritic reactions have been tried at the Museum. These include impregnation with acetone-soluble consolidants or shellac, placement in a dessicating chamber, and even coating fossils on exhibit with fiberglass. None have met with consistent success. During 1957 a fragmentary dinosaur bone was collected from the basal Hornerstown Formation at the Inversand Company pit in southern New Jersey (Baird, 1964). This bone (NJSM 11880) was treated by immersion in molten beeswax by one of the authors (AJ). The bone remains unaffected by pyritic deterioration. Because of the continuing stability of NJSM 11880 it was decided to evaluate the usefulness of beeswax for conservation of other pyrite damaged fossils.

NJSM SPECIMENS INCLUDED IN THIS STUDY

Four specimens from the upper Navesink Formation at the Inversand Company pit (of Hungerford and Terry, Incorporated) in southern New Jersey are included in this study.  Bones from the Navesink  often contain iron sulfides. Specimens in this study all were damaged by pyritic reactions. Prior to treatment they gave off the strong sulfurous odor characteristic of pyritic deterioration. Following treatment none did so.  Four vertebrae from NJSM 11052 were treated first to demonstrate applicability of wax impregnation to deteriorated bones.

The first specimen treated was an uncatalogued skull of Thoracosaurus neocaesariensis collected in June of 1934. The mandibles were in excellent condition when photographed with Dr. Charles Mook in 1940 (Figure 1). By the 1980's deterioration had proceeded so far that the bones were nothing but a pile of splinters and dust (Figure 2). Dessicants had not halted their deterioration. Paraffin treatment has stabilized the bones.

NJSM 11052, a partial skeleton of Mosasaurus maximus, was collected in 1961, and cited by Russell (1967). Consolidants had not prevented damage to the skull bones as the iron sulfides in them oxidized, although their deterioration was less advanced than that of associated vertebrae. NJSM 11052 is a figured specimen, and its long-term conservation is of obvious importance. 

NJSM 9827 (formerly NJGS), a fragmentary skull of Prognathodon rapax, was excavated in 1938 and made the type of Ancylocentrum hungerfordi (Chaffee, 1939), a junior synonym of P. rapax (ref.). In 1984 Donald Baird repaired severe pyritic damage by soaking the bones in thin shellac and reassembled them. However, pyrite deterioration continued, and new cracks had developed by 1996.

NJSM 11053 is a very fine skull of Mosasaurus maximus on exhibit at the Museum. Collected in 1961, it was prepared and mounted for the Museum by Frank Goto and Donald Baird of Princeton University. After installation NJSM 11053 was coated with polyurethane and fiberglass by Steven Garots to halt pyritic deterioration. Unfortunately, some deterioration continued. Open mounting on the gallery wall made the skull vulnerable to fluctuating humidity and temperature in the hall. Fresh pyritic damage was noted while moving the skull for a special exhibit, and dilute acetone soluble consolidant was applied to cracked areas. Concern about long-term stability of this skull helped prompt the current study.

All but one of the specimens in the study were treated using beeswax. Skull bones were treated individually, except in the badly deteriorated Thoracosaurus skull. Treatment with wax appears to have stabilized the fossils. All will be monitored to determine if they remain stable after treatment.

HISTORICAL REVIEW

Some early collectors (Buckland, cited in Howie, 1986) used beeswax in the conservation of vertebrate fossils. Natural consolidants and adhesives (e. g. animal glues, beeswax, and shellac) were later replaced by petrochemical-based consolidants, cellulose nitrate adhesives, or synthetic resins such as polyvinyl acetate (white glues). Consolidants and adhesives with better long-term stability, have replaced earlier synthetic products. The history of consolidant use has been reviewed by Howie (1986) Shelton and Chaney (1994), and Cifelli (1996).

Modern synthetics have definite advantages over natural materials. Among these are excellent long-term stability, since they do not polymerize with age. They are not subject to biological deterioration. They are formulated to be non-acidic. They are easily removed from fossils.  Removal from fossils can be difficult with natural materials (particularly waxes) and also with white glues and epoxy resins. Modern consolidants have known chemical compositions.  Natural consolidants may vary in composition from batch to batch.

DIFFICULTIES WITH USE OF BEESWAX

Natural waxes (beeswax, etc.) are no longer generally recommended for original treatment of vertebrate fossils (Rixon, 1976; Shelton and Chaney, 1994). They are difficult to remove from fossils. Waxes make it difficult or impossible to use other adhesives to repair breaks. Repair of small breaks can be accomplished using the wax itself as an adhesive, but large breaks can only be repaired by drilling and pinning or by first laboriously removing the wax. The chemical composition of beeswax varies even within a hive (Warth, 1956; Eckert and Shaw, 1960; Vivian, 1986; Meyer, 1987). No two batches will be identical. The heat needed to apply wax treatment can soften PVA (Madsen, 1996), which could result in distortion of glued areas. Paraffin wax shrinks as it cools (Wolberg, 1989), but beeswax does not (Warth, 1956). Beeswax should not cause shrinkage damage to fossils.

TREATMENT METHOD

Beeswax treatment is accomplished by immersing the fossil in molten beeswax. The wax bath and fossil are slowly heated to 100oC to drive off water trapped in pore spaces. The bath is then gradually heated to 115oC to drive bound water from the product sulfate minerals which are causing the fossil to crack. Fossils badly affected by pyritic reactions can be heated to 125-135oC to dehydrate the sulfates, leaving only the most stable form, szomolnokite. Heat is maintained until the wax bath ceases to bubble. The fossil and bath are then cooled until the beeswax begins to solidify. The fossil, in its lifting basket, then is removed from the bath and drained of excess wax. Fragile fossils can be left in the bath until the wax is cooler, so that wax is retained in their pore spaces to strengthen them. Surface wax can be removed, after the fossil is completely cool, using wooden scrapers or steel wool. Paper toweling can be used to remove wax softened with a heat gun (gently applied) or mineral spirits.

Fossils often require pretreatment before they are immersed in wax. Some have been heavily coated to prevent pyritic reactions. It is necessary to remove the coating or create openings in it through which wax can enter the fossil. Acetone-soluble coatings are easily removed. The fiberglass-coated bones of NJSM 11052 (Mosasaurus maximus) could not be cleaned with acetone, and access for the wax was provided by drilling small diameter holes (1/32 to 1/8 inch) through the resin coating and into existing breaks in the fossil. Access holes were filled in with wax after treatment. Fragile fossils should be tightly wrapped with gauze before being immersed in beeswax, particularly if they have cracks filled (and held together) by product sulfate minerals. Gauze is removed from the cooled fossil by using a heat gun to gently free it from the surface layer of wax.

PURPOSE OF THE STUDY

The museum is attempting to develop a conservation method for pyrite-damaged fossils that is easily accessible to amateurs. We are trying to keep costs to a minimum by using readily available equipment such as large pots or roasting pans to heat the wax. Temperature of the wax is monitored using a meat thermometer. We find that this simple apparatus works well.  Larger baths can be constructed for very large bones. We advise keeping a fire extinguisher on hand in case foaming or bubbling during heating causes wax to splash onto the heating elements.
Polyethelene glycol (a synthetic wax) was used to stabilize Iguanodon fossils from Nehden (Norman, 1986, 1987). Unfortunately, PEG is somewhat more expensive than beeswax, and may be harder for the amateur to locate. Filtered unbleached beeswax costs about $4.00/lb from our suppliers. Carbowax (PEG) costs $150.00 for 10 lbs or $250/45lb bucket  (or about $5.56/lb). The bulk price is only slightly higher than that of beeswax, but smaller quantities are much more expensive. Carbowax is available from Union Carbide Corporation. Prices were quoted as of 9/27/1999.

POTENTIAL USES OF BEESWAX IN CONSERVATION

While recognizing the limitations and difficulties associated with beeswax, we believe it can be useful for salvaging fossils that are deteriorating due to pyritic reactions. Older collections often have many such fossils, some already very badly damaged by pyritic oxidation. Some of the affected fossils are historically or scientifically significant. If nothing is done to save them, they will eventually be reduced to piles of fragments and dust. 

One potential advantage of using beeswax to treat badly deteriorated vertebrate fossils is that the heat required to melt the beeswax will also dehydrate sulfate product minerals. These sulfates occupy more space than the pyrite or marcasite from which they are derived.  Dehydration of the sulfates reduces their volume slightly, and thereby reduces expansive pressure within the fossil. This pressure causes the cracking associated with pyrite disease. The monohydrate sulfate (szomolnokite) ultimately produced by heating is relatively stable, and is unlikely to react further. Heating fossils to temperatures above 100oC will drive off water trapped within them, and help limit further pyritic reactions.

Waterproofing fossils is not currently regarded as a desirable treatment method (Shelton and Chaney, 1994).  It proved to have disastrous consequences in the case of the Bernissart Iguanodons (Norman, 1986).  We feel that sealing pyrite-damaged fossils with beeswax can be justified, however, to stop ongoing deterioration of specimens which will otherwise be lost to science. The treatment process used drives off both water trapped in pore spaces and bound water in the product sulfates. Our experience with pyrite damaged specimens in the NJSM collection suggests that fossils that are badly deteriorated from pyritic reactions cannot be saved by less drastic methods. Fossils should never be sealed unless they are thoroughly dry, or deterioration will continue (Norman, 1986).

Carbowax (PEG) is usually applied at slightly lower temperatures than beeswax. It melts at about 50oC (Rixon, 1976) and is usually applied at 60oC (Norman, 1986). Beeswax melts at 64oC, and can be heated to over 200oC. We commonly treat specimens with beeswax at 105-115oC. Temperatures up to 135oC are used when pyrite deterioration is advanced.  Lower temperatures are less effective at driving bound water from product sulfate minerals. Carbowax is a viable treatment for pyrite damaged fossils (Norman, 1986), and (being water-soluble) can eliminate trapped water as a source of future pyritic reactions without the need to treat fossils at temperatures higher than 100oC.  It is more easily removed from fossils than is beeswax.  Use of PEG is preferred to use of beeswax in most museum settings. Cost and supplier accessibility make beeswax more readily available to amateur collectors.

RECOMMENDATIONS

We do not suggest that beeswax be used for any purpose except treatment of fossils that contain microcrystalline pyrite, which presents a serious danger to the long-term survival of these fossils (Shelton, 1994). We recommend that beeswax be used only on fossils that are already damaged by pyritic reactions, particularly those that have continued to deteriorate despite attempts to stabilize them using other methods. In these fossils we feel that beeswax can be used as a salvage measure. Proper use of modern synthetic consolidants and storage in humidity-controlled facilities is preferred for specimens that have not yet been affected by pyritic decay. Beeswax treatment cannot be applied to water saturated wood.

ACKNOWLEDGEMENTS

We thank Sally Y. Shelton (National Museum of Natural History-Smithsonian Institution) for reviewing the manuscript.

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BEESWAX AS A CONSOLIDANT short version

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