Fossil Preparation and Preservation Techniques
Fossil Preparation and Preservation Techniques
Finding a fossil is just the beginning. Proper preparation and preservation techniques transform a rough rock-bound specimen into a displayable, scientifically valuable object. Whether you are a casual collector or an aspiring preparator, these techniques will help you care for your finds.
Field Collection Best Practices
Good preparation begins in the field:
Document before collecting: Photograph the fossil in situ (in its original position) from multiple angles. Record the exact location (GPS coordinates if possible), the rock formation, the orientation of the specimen, and any associated fossils nearby. This contextual information is often more scientifically valuable than the fossil itself.
Excavate carefully: Do not try to pry a fossil directly from the rock. Instead, remove a generous block of matrix (surrounding rock) with the fossil inside. It is always better to take too much rock than too little — you can remove excess matrix later in a controlled setting.
Wrap and label immediately: Wrap specimens in newspaper or bubble wrap as soon as they are collected. Label each package with a unique number that corresponds to your field notes. Many valuable fossils have been rendered scientifically useless by losing their provenance information.
Mechanical Preparation
Mechanical preparation uses physical tools to remove rock matrix from fossils.
Hand Tools
Dental picks and scribes: Precision tools for removing matrix grain by grain around delicate features. The most common preparation tools, available from dental supply companies.
Needle in a pin vise: For extremely fine work around eyes, sutures, and thin edges.
Rock hammer and chisel: For initial rough removal of large amounts of matrix. Work from the outside in, always directing force away from the fossil.
Air Scribes and Pneumatic Tools
Air scribes (pneumatic engraving pens) are the workhorse tools of professional preparators. They vibrate a carbide or steel tip at high frequency, chipping away matrix with precision and speed far beyond hand tools. Different tip sizes are used for rough and fine work.
Air abrasive units (micro-sandblasters) use a stream of fine powder (usually sodium bicarbonate or aluminum oxide) propelled by compressed air to gently remove matrix. Excellent for cleaning surface detail without scratching the fossil.
Chemical Preparation
Chemical preparation uses acids or other solutions to dissolve matrix while leaving the fossil intact. This works because fossils and their surrounding rock often have different mineral compositions.
Dilute acetic acid (5–10% vinegar or lab-grade acetic acid) dissolves limestone (calcium carbonate) while leaving silicified or phosphatic fossils unharmed. This is the standard technique for extracting fossils from limestone.
Dilute formic acid (5%) works similarly but more aggressively. Used for tougher limestone matrices.
Thioglycollic acid can remove iron staining from fossils.
Important safety note: Always use acids in a well-ventilated area, wear gloves and eye protection, and neutralize acid waste before disposal.
Consolidation and Repair
Many fossils are fragile and require stabilization:
Paraloid B-72: An acrylic resin dissolved in acetone, used by most museums as a consolidant. Applied by brush or dropper, it penetrates porous bone and shell and hardens as the solvent evaporates. Reversible with acetone, making it the preferred choice for scientifically important specimens.
Cyanoacrylate (superglue): Used for quick repairs and joining broken pieces. Penetrates cracks well. Not easily reversible, so use sparingly on important specimens.
Epoxy putty: For filling gaps and reconstructing missing areas. Should be a different color than the original fossil to distinguish reconstruction from original material.
Cleaning Techniques
Brushing: Soft brushes (old toothbrushes, artist's brushes) remove loose sediment without scratching.
Ultrasonic cleaners: Small ultrasonic baths vibrate at high frequency, loosening dirt from surface details. Effective for small, sturdy specimens.
Water washing: Gentle running water with a soft brush removes loose sediment. Avoid prolonged soaking of porous specimens (especially bone), which can cause swelling and cracking.
Storage and Display
Labeling: Every specimen needs a unique catalog number linked to provenance data (collection location, date, collector, formation). Use acid-free paper and archival ink.
Storage containers: Acid-free boxes or plastic containers with foam padding. Avoid cotton wool, which can catch on delicate features.
Display: UV-filtering glass or acrylic protects specimens from light damage. Keep specimens away from direct sunlight, heat sources, and high humidity.
Pyrite disease: Fossils preserved in pyrite (iron sulfide) can deteriorate when exposed to humidity — pyrite oxidizes, producing sulfuric acid that crumbles the specimen. Store pyrite fossils in low-humidity environments with silica gel desiccant packets.
When to Seek Professional Help
Some specimens require professional preparation:
- Vertebrate fossils embedded in hard matrix
- Specimens with extensive cracking or fragility
- Scientifically significant finds that need museum-quality preparation
- Large specimens requiring jacketing (plaster encasement) for transport
Many natural history museums offer preparation workshops, and fossil clubs often have members with preparation experience willing to advise beginners.
Resources
- Your local geological society or fossil club
- Natural history museum preparation labs (many offer public tours)
- The Eon Codex collection — see what properly prepared specimens look like
- The Fossil Identification Guide — determine what you have before preparing it