Preparation and Conservation
Until a time machine is invented, fossils represent the only information we have about extinct animals. The information contained in fossils can be developed and enhanced by proper preparation techniques. This information can also be preserved for future generations through proper conservation and storage. The topics in these pages will help you to accomplish the goals of both preparation and conservation of fossil specimens. This web page was written by former museum fossil preparator Russell McCarty in the late 1990s and then periodically up-dated. The information posted here is intended to assist the avocational paleontologist help preserve and conserve their specimens. The Florida Museum of Natural History and its staff are not responsible for any damage to fossil specimens resulting from misinterpretation of the presented materials.
- Preparation with Mechanical tools
- Preparation and Treatment of Sub-fossil Bone
- Removing Iron Deposits from Artifacts and Fossil Bone
- Preparing Modern Skeletons
Consolidants, or hardeners as they are more commonly called, are often the collector's first line of defense against deterioration of specimens in their collection, especially those specimens comprised of poorly mineralized bone so often found in the Pleistocene river deposits or coastal marls of Florida and the rest of the Southeast. By definition, a consolidant is a resin which has been dissolved in a solvent. Common solvents are water, acetone, alcohol, and toluene. Consolidants are generally available in two forms: 1) pure resins, and 2) emulsions. Pure resins consolidants are resins which have been dissolved in a solvent, such as Butvar (polyvinyl butyral) granules dissolved in acetone. Consolidants dissolved in acetone should only be used on dry specimens, since even a small amount of moisture in the specimen can react adversely with the consolidant destroying its desired properties. Museums in the U.S. and Europe stick with a few tried and true consolidants which are known to have a low tendency for crosslinking and which do not lose their consolidant properties over time. Chief among these are polyvinyl butyral (Butvar), a thermoplastic resin, and Acryloid B-72, an acrylic resin. PVA (polyvinyl acetate), used as a pure resin is still available, but most users have switched to Acryloid B-72, which is harder, more durable, and exhibits less flexibility. Pure resins are mixed with their solvents to form a very thin, watery solution which is then applied to the specimen (or the specimen is immersed in the solution). Thin and watery should be stressed. The idea is to get the resin where it's needed, and in order to penetrate the specimen's surface and carry resin down into the interior of the fossil bone, the consolidant must be thin or else it will be deposited on the surface of the bone only, like shellac or varnish used in the past. Those treatments may have protected the surface, but did little to strengthen the whole bone.
The second class of consolidants, the emulsions are mainly used to treat wet or moist specimens. Emulsions are suspensions, in water, of a resin and solvent solution, and like Elmer's Glue, a popular polyvinyl acetate emulsion, are generally white, milky mixtures. As consolidants go, emulsions are not as desirable as pure resins. It is hard to reverse emulsions once they have dried, and virtually impossible once they have cross-linked with exposure to ultra violet light from the sun or from fluorescent bulbs. Emulsions also have a tendency to turn yellow with age and cross-linking, but these negatives characteristics aside, there is probably no better treatment for soft, wet bone. Brand names such as Rhoplex AC33, CM Bond M3, and Union Carbide's AYAF, are all good general purpose PVA emulsions. They are normally mixed with water in a ratio of 15 to 20 parts emulsion to 85 to 80 parts water. This mixture can be brushed on the bone, or the specimen can be immersed in the consolidant mixture. As mentioned earlier, Elmer's Glue, is a type of polyvinyl acetate emulsion, and can be used on wet specimens. Because proprietary (commercial) brands such as Elmer's generally keep their formulas secret, and even periodically change their formulas, museum conservators do not like to use these commercial PVA emulsions. However, Rhoplex, CM Bond M3 and Union Carbide AYAF PVA emulsions are specifically designed and sold for conservation purposes.
When considering the question of whether to use a consolidant on a specimen or not, the collector should remember that not all specimens require consolidation. The most important axiom of conservation is: Minimal intervention is best. In other words, do as little as possible to a specimen that will change its nature. When dealing with sturdy wet specimens, the best approach may be to place the specimen in a slow-drying chamber, (see Preparation and Treatment of Sub-fossil Bone) rather than treating the specimen with a water based emulsion resin like Rhoplex or CM Bond M3.
Everyone who collects or works with fossils, has, at some time or other used adhesives, or glues to restore or repair a specimen. Over the past hundred or so years that fossil collecting has been a valid scientific pursuit, as well as a popular past-time for collectors, a variety of adhesives have been used to glue fossil bone. The adhesives in use at any given time during this period reflected the existing state of chemistry and technology, so naturally, the diversity and quality of adhesives has changed through time. From the viewpoint of the strict conservationist, all adhesives used on museum specimens, should be reversible; however, from the practical standpoint of the preparator, that is not always possible. For instance, when recovering wet fragile specimens from moist environments, the melted carbowax method might be the only way to recover the specimen, but it is not reversible without destroying the integrity of the specimen. Similarly, when repairing a broken elephant femur, which may be studied and handled, the preparator might opt for using epoxy cement to prevent the specimen from continually re-breaking. These are judgment calls that only the particular set of circumstances can determine.
From the earliest times, animal glues made from bones, fish, and hides were the mainstay for fossil repair. In fact animal glues, which probably date back to prehistoric times, were used for just about every adhesive need, and can still be purchased today. Due to their inherent problems such as yellowing, brittleness and instability, they should no longer used on fossils. Consisting mainly of collagen/protein slurries, animal glues are also quite tasty to a variety of pests. This class of adhesives is mentioned because of its long period of use. In museums and at fossil auctions, it is not uncommon to find specimens which have been repaired with these glues. Alcohol is a solvent for these glues, but many of the older specimens will require a good soaking before the glued joint will dissolve.
The 20th Century has given us many new classes of adhesives, all of which are organic polymers, large complex molecules, formed by chains of simpler molecules called monomers. Chemists may extol the virtues of the newest glue from their laboratories, but only time can judge the effectiveness and longevity of an adhesive. Many turn yellow with age or are prone to brittle breakage, where even a slight jar or shock will cause the glued joint to break. Other polymers may cross-link with time or upon prolonged exposure to ultraviolet light causing shrinkage that can seriously damage a fossil which has been repaired with them. Most of these polymers have unique properties and characteristics which will make some better for certain uses than others.
Butvar, polyvinyl butyral, made by Monsanto, is one of the most widely used adhesives in paleontology. Shrinkage is minimal and the set glue is fairly easy to reverse with the proper solvent. Monsanto produces three grades of Butvar, B72, B76 soluble in acetone, ethyl alcohol, or ketone, and B98 soluble in ethyl alcohol.
With the possible exception of the Butvars, the acrylic polymers may be the most popular adhesives used in paleontology. Trade names such as Acryloid B72 and Lucite are familiar products to fossil preparators. Their reversibility and long term integrity make them ideal adhesives. Most use common solvents such as acetone, ethyl alcohol, or carbon tetrachloride.
Polyvinyl Acetate Emulsions
Polyvinyl acetate emulsions are familiar as Elmers and other white glues like CM3 Bond and Vinamul. While they have been used for many years to repair fossils, most professionals believe the drawbacks of these glues, such as poor reversibility, acid generation, and the low temperatures at which they change from hard glass-like bonds to weak plastic bonds (glass transition temperature, TG ), make them poor candidates for fossil repair. Their best use may be as consolidants for wet specimens.
Epoxy resins, one of the spin-offs of the great "Space Race", have a limited role in fossil repair. Since they are considered non-reversible, a glue joint made with epoxy resin is a permanent bond. Corrections or adjustments range from the difficult to the impossible once the glue has set. However, there are certain circumstances when the preparator is reasonably sure that the bond will not have to be undone and where extreme strength is needed, that may require the use of epoxy resin adhesives. It is possible to soften and reverse a bond with steam. This can be generated with water heated to boiling in a flask. A rubber flask stopper fitted with a glass tube should be inserted in the flask. Attach a piece of plastic tubing, one or two feet long, to the glass tube. The plastic tubing can direct the steam to the bond which is to be reversed. Epoxy adhesives are available almost everywhere and under many trade names.
Cyanoacrylate "Super Glues"
Another class of Space Age adhesives used to repair fossils are the 'super glues', or cyanoacrylates. Their characteristics, which include rapid setting time and strength, have made these adhesives increasingly popular for fossil repair; however, since they are so new (dating only from the 1980s), our knowledge of their long-term efficacy is limited. A definite drawback is the difficulty of reversing bonds made with cyanoacrylates. A number of companies manufacture these adhesives under the names of Zap, Hot Stuff, and PaleoBond, and others. PaleoBond is a fairly new product that was developed specifically for fossil repair. PaleoBond, Hot Stuff, and Zap generally come in several grades or viscosities. Thin grades are best for gluing non-porous joints. Thicker grades are better for gluing cancellous bone or where gap filling is required.
The last class of adhesives mentioned here are the cellulose nitrates. These are familiar as Duco Cement, Randolph's, and Glyptal. Duco and Randolph's and other commercial cellulose nitrate adhesives are not good candidates for fossil repair. All cellulose nitrate adhesives tend to yellow with age and exposure to UV light, and most have the added problem of severe shrinkage which can damage specimens. Acetone and ethyl acetate are common solvents used with these adhesives, but reversibility is difficult. Glyptal, a Canadian product, has been used for many years by preparators, and is an acceptable adhesive, although it tends to yellow with age. Glyptal also is fairly reversible with acetone.
Fossil specimens, whether they are in scientific collections, or in a private collection must be considered valuable and irreplaceable objects. As such, conservationally sound and approved adhesives should be used wherever possible. For the sake of expediency, the preparator is sometimes tempted to use whatever adhesive is most handy. The cost of a hasty decision may not be realized until five years later when a valuable specimen is pulled apart by shrinking glue.
While fossils from many locations can be easily prepared with hand preparation tools such as dental picks, brushes, spatulas, pin vises---even hammer and chisel, specimens from other locations require the use of mechanical preparation tools. This category of tools includes those powered by electricity or pneumatically by compressed air. There are several different categories of mechanical preparation tools, each with its particular advantages and special uses. Air abrasive devices, miniature air hammers, electric etcher/engravers, and rotary grinders are discussed on these pages.
Air Abrasive Devices
These devices are scaled down sand blasters which eject a stream of grit-like particles propelled by pneumatic pressure. Air abrasive units are ideal for detail work when preparing micro-fossils. This type of tool is also good for cleaning up invertebrate fossils found in limestones and other hard matrices. As a general rule, the air abrasive is used only after the bulk of the matrix has been removed with other mechanical or hand tools. It takes just a little bit of experience to validate this rule. Even using the hardest grits and highest pressures, removing matrix with an air abrasive can be slow work. It is also a very costly way to remove bulk matrix, because the grits used in these devices are fairly expensive and cannot be recycled. For these reasons, air abrasive devices are used mainly for finishing work. An example would be using the air abrasive to clean up the teeth and remove any thin residual matrix from a jaw that has had most of the matrix removed by other methods. The preparator will have to experiment with the devices in order to find the uses best suited to your needs.
Two companies produce most of the air abrasive systems used by preparators, S.S. White and Crystal Mark. S.S. White has been the air abrasive business for the past fifty years and markets complete systems for industrial or laboratory use. Crystal Mark, a newer company in the business manufactures an economical, rugged and dependable product that is backed up by a responsive support staff for service, sales, and repair. These devices remove matrix by emitting a stream of grit propelled by compressed air. Cutting by these tools can be varied by adjusting the air pressure, thus raising or lowering the velocity of the air stream, or by changing nozzles, thus altering the spray pattern of grit emitted, or by using grits of different hardness. Grits range from the hardest grades of aluminum oxide through descending grades of hardness such as glass, powdered dolomite, sodium bicarbonate, down to the softest grits like powdered walnut shell and cork.
As the preparator learns with the first use of the air abrasive device, the stream of grit will take bone away as well as matrix, especially if the nozzle is kept in one spot for more than a few seconds. The trick is to move the nozzle around frequently, back forth over an area, and to vary the angle of attack. This will maximize the cutting power of the grit. The hardest grits, like aluminum oxides, will cut through hard matrix like shales, slates, and sand and mudstones. Softer grits such as sodium bicarbonate are used for cleaning up invertebrate fossils like echinoids and crabs found in the soft limestones of Florida. Using a grit which is too hard for the job at hand usually results in damage to the specimen, so the preparator who uses an air abrasive device should always keep grits of several different hardnesses on hand.
Different nozzles may be fitted to the hand held stylus. Some nozzles have tight grit spray patterns which are better for deep cutting. Other nozzles are fan shaped and fan out the grit to cover a wider area, producing a gentler cutting action. The beginner should practice with an expendable specimen until the art of preparation with an air abrasive is mastered. For safety, the operator should use a grit recovery system, and wear a particulate mask, and of course use the nozzle in a work chamber. Air abrasive systems are expensive. A minimal system, in which you build your own chamber and grit recovery system will cost around $2000 for the air abrasive unit itself. Every air abrasive system, especially those located in humid environments, should have an inline moisture trap. They are easy to install and will prevent moisture in the airlines from clogging the the unit with dampened grit.
Miniature Air Hammers
Like many products developed primarily for industrial applications, fossil preparators quickly discovered miniature air hammers were the perfect tool for removing hard matrix from fossils. These pneumatic tools operate with a reciprocal motion of a hard conical stylus, that cycles up to 40,000 motions per minute. The force applied by the stylus, and the number of cycles per minute can be adjusted to the needs of each particular task. In this country there are three companies which produce miniature air hammers: Chicago Pneumatic, which produces the air scribe CP 9361, and a newer model made expressly for preparation, the AERO, and the Ingersoll Rand EP5O Air Engraving Pen.
As with all mechanical tools, these devices will damage fossils as easily as they cut through matrix, so that care must be taken when learning to use these tools. When working with hard matrix, this tool can reduce preparation time to a fraction of that accomplished by other methods. The rate of matrix removal is controlled by adjusting the amount of air which in turn controls the number of reciprocal motions per minute the tool will make. The hand held stylus can also be fitted with different shaped chisels which have different cutting characteristics. The best matrix cutting technique is to work on or near the edges of the rock, rather than trying to dig a hole in the center of the matrix. Chisels can be damaged by digging a hole in the matrix and attempting to pry the piece of matrix away. Very little force is required, in fact, barely enough to hold the stylus, for the air hammer to operate at maximum efficiency. When working near teeth or a fragile part of a specimen, it is advisable to slow down the motion and force of the air hammer to avoid excessive vibration or other damage. By changing the angle of attack from vertical to almost horizontal, the chisel goes from a digging, high impact position to one of rubbing or gently vibrating the matrix. At some point, especially with fragile specimens, the preparator might be advised to switch to another less traumatic method such as the air abrasive tool or the electric etcher/engraver.
If you already have an air compressor, a miniature air hammer system can cost anywhere from $140 to $350 to set up. Since these tools are made for the metal working industry, their manufacturers recommend oilers which need a constant stream of oil into the air lines; however, for fossil preparation, it is sufficient to add 6 to 8 drops of lubricating oil to the air lines each day you are using the tool. When using air hammers, the operator must wear eye protection at all times to protect from flying rock chips, or a work chamber can be built using plexiglass or glass, and wood.
Electric Etchers or Engravers
Fragile or delicate specimens require a gentler touch than can be provided by the pneumatic mini air hammers. Electric etcher/engravers, like the miniature air hammers use a reciprocating stylus to remove hard matrix. They have nowhere near the force of their pneumatic cousins, the air hammers, but with a few modifications they can provide an inexpensive substitute for the more expensive tools. To make them more effective at removing matrix, you must first remove the stylus that comes with the etcher and throw it away---it's useless. Now get a 1/8 inch drill bit and grind down the tip to a long, thin, tapering point. Just insert this newly made stylus into your etcher and you are ready to go. You will find it much more effective for removing matrix than the stock stylus sold with the etcher. Goggles, or a work chamber should be used when operating these tools. Dremel etcher/engravers, are available at most hardware and building supply stores for less than $30. The preparator can make a number of different shaped styluses, each with a specific application, by grinding drill bits, old dremel bits, or used dental drill bits into the desired shape. As with most power tools used for removing matrix, goggles, or some form of eye protection should be used to protect the eyes from flying rock chips. A number of other companies also manufacture this type of tool, including the Burless Vibrograver.
Pneumatic Rotary Grinders
Rotary grinders use a rotating bit, instead of percussion and vibration, to remove matrix from fossils. Their use is indicated where excessive force or vibration would damage a specimen. The miniature air grinders such as the Starlite are close relatives of the drills used by dentists and rotate at speeds up to 340,000 revolutions per minute. Because of this high rate of speed, they can easily damage bone. Similarly, with the Pneumatic Etcher/Engravers, the optimal use of these tools is achieved after the bulk of overlying matrix has been removed by other means. The rate and degree of matrix removal with these tools is controlled by the type of bit, or burr used, and the revolution speed which the operator controls with a foot pedal. If you already possess an air compressor, a Starlite system can cost in the neighborhood of $250 to $350 dollars.
Electric Rotary Grinders
The two categories of electric rotary grinders are the self contained hand-held grinders such as the Dremel rotary grinders which can be purchased at most hardware, hobby, or building supply stores, and the flexible shaft grinders like the Foredoms which are usually found in specialty catalogs. The hand held grinders are simple and easy to use. A large variety of burrs, grinding bits, and cutting wheels are available for them. The speed (revolutions per minute) are controlled by a switch which has variable positions for different speeds. The flexible shaft grinders transmit power from the motor to the grinding head through a flexible metal shaft that is several feet long. The speed is controlled by attaching the flex cable to one end of the motor, or to the other geared end which produces a different speed. The flex shaft grinders also have optional foot pedal, variable speed controls that act much as an accelerator pedal.
Rotary grinders, whether pneumatic or electric, are very useful in a prep lab, but are probably more of a finishing or touch up tool than one to use for major matrix removal. Many preparators prefer the hand held Dremel type grinders to the flex shaft grinders because there are fewer problems with cables that have a tendency to kink and have to be greased frequently. Hand grinders are also able to get into tight spots that flex cables are unable to reach. An added plus for hand grinders is that they are much less expensive---averaging about 1/5 the price of the flex shaft models. In some situations, where long periods of use are required to prepare a fossil, flex shaft models have distinct advantages. They have larger, more powerful motors, so greater cutting pressure can be applied to the matrix, and the larger motors outlast the smaller hand held grinders.
SUPPLIERS OF MECHANICAL PREPARATION TOOLS
- Kingsley North, Inc. Rotary grinders, hand held and flex shaft grinders. Call for catalog. 910 Brown St. Norway, Ml 49870 Tele: (1-800) 338- 9280
- Chicago Pneumatic Air Tools Pneumatic engravers (Airscribe) 2200 Bleecker St. Utica, NY 13503 also from: Cameron & Barkley Co., P.O. Box 26789, Jacksonville, FL 32218 (904)757-0211
- Starlite Industries, Inc. Pneumatic rotary grinders 1111 Lancaster Ave. Rosemont, PA 19010 Tele: (215) 527- 1300)
- Local Building Supply or Hardware Stores Electric Rotary Grinders Electric Etcher/Engravers
- Crystal Mark, Inc. Air abrasive systems 613 Justin Ave. Glendale, CA 91201 Tele: (1-800) 659- 7926
PREPARATION AND TREATMENT OF SUB-FOSSIL BONE
The fossil collector may encounter specimens that seem poorly preserved, with little or no mineralization. These specimens often have short lifespans once they are removed from the matrix in which they are found, thus, special care and treatment is necessary if they are to be preserved as viable specimens of a scientific or personal collection. In Florida's rivers, and in those of other southeastern states, this type of bone, generally referred to as, sub-fossil bone, may represent the most common type of bone in many fossil collections.
Living bone consists of collagen fibers and the mineral hydroxyapatite. Sub-fossilized bone, which is primarily from the Pleistocene and Recent Epochs retains a fair amount of the organic material (collagen) and the original mineralized bone (hydroxyapatite). You can easily test for collagen yourself; by holding a piece of Pleistocene bone against a grinding wheel, or in a flame. If it gives off a bad odor (like burning hair), it contains collagen. To maintain its integrity, sub-fossil bone needs to be kept in a stable environment. Once it is removed from the matrix in which it is found, it is likely to deteriorate rapidly, especially, if it is wet, and the bone is subjected to extreme fluctuations of temperature and humidity.
There are two possible approaches to preserving wet specimens, both of which, can be done at the same time, if necessary. The first is the use of water based consolidants. These can be applied by brushing, immersing, spraying, or vacuum impregnation.. The most frequently used water based consolidants are water soluble plastics such as polyvinyl acetate emulsions (white glues) and acrylic emulsions such as Rhoplex. These are mixed in a ratio of about one part consolidant to 10 parts of water. Water based consolidants, such as Rhoplex, polyvinyl acetate emulsions, should never be applied to or completely dry specimen, because the high water content of the consolidant will cause the dry specimen to swell and crack multi-dimensionally. Instead, dry specimens should be preserved with organic solvent based consolidants such as Butvar or, or Acryloid B72.
The second approach to treating wet specimens is the slow, controlled drying method to prevent cracking and delamination. Old fish tanks made satisfactory drying chambers. The wet specimens can be placed in the tanks and plastic food wrap placed over the top with a rubber band around the perimeter to hold the plastic wrap tight. A few slits, or flaps cut in the wrap will allow you to control the rate of drying. For larger specimens, an inexpensive, but functional drying box can be easily constructed by placing a piece of clear plastic sheeting, such as Visqueen, over a sturdy box. Place the wet specimen inside the box and cut a few flaps or slits in the plastic. The flaps will allow a slow, controlled exchange of the moist air in the box with the lower RH (relative humidity) ambient air outside the box. Similarly, a large, clear plastic bag, or a makeshift tent made of plastic sheeting might be used for very large wet specimens. Again, flaps or slits cut into the bag or tent would regulate the air flow. To monitor changes in RH, a humidity gauge can be placed in the containment area along with the specimen. One negative side effect of the slow drying method which keeps the specimen wet for a long period of time is that it fosters mold growth. A periodic spray of Lysol or any fungicide inside the containment area should control the problem of mold growth.
The goal of all controlled drying procedures is to bring the high RH of the wet specimen slowly downward until it matches that of the storage area. Even if a water based consolidant is used to conserve (preserve) a wet specimen, it is advisable to apply controlled drying procedures until the specimen is stabilized to storage environment conditions. Ideally, the optimum storage environment for sub-fossil bone should be in the range of 45-55% relative humidity with a temperature between 65 and 72 degrees. Storage below 50% RH can lead to cracking and shrinking as the specimen dries out. RH above 70% encourages mold and fungal growth which can damage sub-fossil bone. Since both RH and mold and fungal growth are temperature dependent, it is important to keep the temperature in the narrow good range of 65 to 72 degrees.
Once the specimen has been dried and stabilized at room humidity, a non-waterbased consolidant such as Butvar or Acryloid B-72 can be applied if necessary. Please remember that waterbased consolidants should never be applied to specimens which have thoroughly dried.
Particular attention should be given to filler materials used to repair or restore sub-fossil bone. Materials which shrink or expand upon curing should be avoided as either action can damage the specimen. Plaster of Paris should not be used on very dry specimens, since the water in the plaster will cause the specimen to swell and crack. What's good to use? Paper mache and plaster mixed about 50/50 is not too bad, since the mache absorbs most of the water. Epoxy putties, like Magic Sculp, although they are not easily reversible, are OK if the repair is permanent, and not one that is likely to be undone. Butvar or polyvinyl acetate glues can be filled with Cab-O-Sil or silica microbeads to form a stiff paste that can be used to fill cracks and voids. The advantage of these last two fillers is that they are reversible with acetone.
Polyethylene glycol (PEG), or CarboWax, as it is commonly called is a water soluble wax used for preserving wet wooden artifacts. Its use as a consolidant for wet bone has mixed reviews, especially when it is dissolved in water to make a hardening solution for bone. However, it has been used to remove damp specimens from caves or other moist environments by melting the CarboWax and pouring it over the specimen.
One final rule of thumb concerning treatment of sub-fossil bone comes from conservator, C.J. Buttler: 'Once treatment is completed, a specimen should not be placed back into an environment where it will deteriorate again.'
REMOVAL OF IRON COMPOUNDS FROM ARTIFACTS AND VERTEBRATE FOSSILS
Those of you who collect in Florida's northern and central rivers have frequently encountered specimens that would be perfect except for the disfiguring hematitic (iron) stains and encrustations on them. In fact, in some rivers in the Florida Panhandle, this is the norm. Attempts to remove these stubborn deposits, by physical methods, such as grinding or using air abrasive tools, most often results in permanent damage to the specimens regardless of their composition. In 1974, Francis Howie, of the British Museum described a method for removing hematitic matrices from vertebrate fossils by using a dilute aqueous solution of thioglycollic acid. Howie first coated all exposed surfaces of the bone with the resin, polystyrene, to provide a protective barrier. After the resin had cured for six hours, he immersed his specimen in a 5% aqueous solution of thioglycollic acid (19 parts distilled water to 1 part thioglycollic acid). To this solution was added 0.9% calcium orthophosphate by weight. The addition of the calcium orthophosphate is to prevent the thioglycollic acid from scavenging phosphate from the bone. Howie left his specimens in acid for 24 hours. They were then removed, allowed to drain, and then immersed in a 5% ammonium hydroxide (ammonia) solution to neutralize the acid. The specimens were then washed in several changes of water for four days. He then used gentle brushing, and air abrasive to finish removing the deposits.
As you can see, even this "easy" method is fairly time consuming and meticulous. But for an important specimen, the time spent in chemical development would be repaid. My first experiment on removing iron deposits with thioglycollic acid was on a chert tool from the Aucilla River. The chert specimen was so heavily encrusted with iron deposits, that it was hard to discern the true nature or shape of the tool.
I placed the tool in a 5% solution of thioglycollic acid made up as above---except that I left out the calcium orthophosphate. I felt that this was an unnecessary buffer since there was no bone involved. The specimen was left in the acid solution for 48 hours. It was then removed, rinsed in water, and placed in a 5% ammonium hydroxide solution for a few minutes to neutralize the acid. At this point the specimen was placed in a water bath for several hours.The iron deposits had turned to a soft, powdery film that brushed away easily with a soft toothbrush. All traces of the iron deposit was gone. Thioglycollic acid is available from Fisher Scientific supplies at a cost of about $25 dollars per 100 ml bottle. That would make about 2000 ml of 5% solution. When working with any chemicals, one should always read the materials safety data sheets which the suppliers provide and follow all rules for safe usage. Thioglycollic acid produces hydrogen sulfide as it digests the iron compounds. Hydrogen sulfide is a poisonous gas, but familiar to everyone as the smell of rotten eggs and sewer gas. In the small quantities used for removing iron from flint tools, the use of this acid should present few problems, especially if the process is performed in a fumehood or in a covered container placed in a well ventilated room.
Howie's method (Howie, F.M.P. 1974. Introduction of thioglycollic acid in preparation of vertebrate fossils. Curator 17:159-166) has proven successful for many applications and should be reviewed before attempting to remove iron from fossil specimens. Using thioglycollic acid, while applicable to many situations, does have a few drawbacks such as the foul odor produced by the acid. An alternative noncorrosive method which uses no acid was developed by Rob Waller, a Canadian conservationist, and adapted to vertebrate fossils by Blum, Maisey, and Rutzky (Blum, S.D., J.G. Maisey, and I.S. Rutzky. 1989. A method for chemical reduction and removal of ferric iron applied to vertebrate fossils. Journal of Vertebrate Paleontology. 9(1):119-121. This method is a bit more complicated than Howie's method.
PREPARING MODERN SKELETONS
Skeletons of modern animals are extremely useful in helping you identify fossil bones. But preparing clean skeletons from a carcass can be a smelly and potentially hazardous proposition. First of all, you should make sure that the specimen is obtained legally. Almost all wild birds, except game species such as duck, turkey and quail, are protected and their feathers and skeletons can not be legally owned by individuals. The same is true for all marine mammals (whales, dolphins, seals, manatee, etc.) and any endangered species.
For the Florida fossil hunter, having modern skeletons of the following animals will be the most helpful:
- Fish: gar, mudfish (Amia calva), redear sunfish, drum, mullet, grouper or other large marine fish such as marlin or tarpon.
- Amphibians: large bull frog, toad, siren
- Reptiles: snake (several species), alligator (if obtained legally)
- Birds: duck, turkey
- Mammals: opossum, armadillo, and raccoon (the big three in terms of road kills); other potential road kill species are beaver, squirrel (although typically too damaged to be much good), muskrat, rabbit, otter, fox, bobcat, and coyote. Through a hunter you may be able to obtain a carcass of a deer or boar. Through a ranch you may be able to obtain bones or a carcass of a cow, horse, or llama.
Once the carcass is on hand, carefully remove the skin, organs, and as much muscle as possible, but be careful not to scratch or damage the bones. To remove all the remaining soft tissue, there are two basic methods: soaking in water (maceration) or letting small insects do the job. This pamphlet from the University of Arizona provides a good introduction to the basic techniques, although you would want do the entire skeleton and not just the skull. There are also commercial outfits that maintain bug colonies and will clean skulls and bones for you. One example is this company.
If you find a skeleton in the wild, you can use hydrogen peroxide to white the bones.