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Smithsonian National Museum of Natural History
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Drawing of a fossil preparator's hand excavating a juvenile Compsognathus dinosaur from rock, as the little dinosaur comes to life.

When large fossils arrive in FossiLab or in our behind-the-scenes lab, they often are embedded in matrix (rock or loose sediment) and only partly visible. Staff and volunteer preparators ready them for scientific study by using a variety of tools to remove the matrix. They also stabilize the fossils with consolidants and adhesives. This step is critical because most fossils are cracked or broken, and removal of the matrix without stabilization can cause them to fall apart. To prepare the tiniest fossils, called microfossils, volunteers may use a process called "washing and picking" to clean away the matrix and isolate the fossils.

Tools commonly used in fossil preparation are shown in the photo on the right. The choice of tool is determined by the condition of the fossil and the characteristics of the matrix. Scroll down for descriptions of how the tools are used.

An assortment of tools used in fossil preparation.

Tools from the FossiLab tool drawer.

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Air Scribe
 

The workhorse of fossil preparation is the air scribe. Powered by compressed air, it operates like a miniature jackhammer, chipping through the rock matrix that covers the fossils. Tools of different sizes are used for different jobs; the smallest airs scribes, like the one pictured on the right, are used to remove matrix near the most delicate fossils; the largest, which require two hands to control, are reserved for plowing through thick, hard blocks of matrix that contain larger fossils. When the matrix is thinned sufficiently, the air scribe’s impacts often cause the last layers of rock to pop off the fossils, leaving them clean and exposed. When that doesn't happen, we switch to picks and needles to remove the last remnants, sometimes grain by grain.

Since the air scribe is, by design, very destructive, extreme care is taken when using this tool directly adjacent to fossils. Bright lights, magnifying glasses and microscopes help us to avoid damage. To a preparator, nothing feels worse than poking a hole in a fossil!

A video shows an air scribe in use to remove rock matrix from around a fossil leaf

Watch a video to see an air scribe removing rock from around a fossil leaf.

It takes two hands to handle a very large air scribe.

The largest air scribes require two-handed operation. Click to zoom.

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Grinding Tools
 

We use grinding tools when the rock matrix is too hard for air scribes, when a fossil is not robust enough to withstand the vibrations they cause, or when there is not good "separation" between the matrix and a fossil. Grinding tools are powered by small electric motors and have a more gentle, rotary motion. After the matrix is ground down to a very thin layer, picks are used to remove the last bits of rock still clinging to the fossil. If the last bits of matrix cling too tightly, then the grinder has to be used all the way down to the fossil's surface. This is a very undesirable situation because the risk of damaging the surface is high.

The spinning tip of a grinding tool removes red matrix from a fossil bone.

A grinding tool is used when the matrix is very hard, when a fossil is particularly fragile, or when the rock "sticks" too tightly to a fossil. Click to zoom.

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Picks and Needles
 

Picks and needles are used when the matrix is too soft to chip away with an air scribe, or the fossil is too small and delicate. Fossil preparators use various shaped picks and probes for different jobs. Pin vises (pencil-like hand tools that hold tungsten-carbide needle-like pins) are useful for gently scraping matrix off a fossil and for picking matrix out of hard-to-reach crevices. Dental picks can be also used to scrape sediment away. When sediment must be removed from a fossil grain by grain, a preparator may resort to using a very sharp sewing needle.

A video shows a pin vise being used to remove rock matrix from a fossil dinosaur bone

Watch a video to see how a pin vise is used to remove matrix from a dinosaur bone.

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Brushes
 

Brushes of assorted sizes are used to clean and sort fossils. Big, soft brushes are used to sweep rock dust and debris away from fossils as they are being prepared with other tools, and stiff-bristled brushes (such as toothbrushes), are useful for preparing fossils embedded in relatively soft matrix. FossiLab visitors often see another use of brushes; we use small, moistened brushes to transfer microfossils from under microscopes to slides or small boxes, taking advantage of the attractive forces between solid surfaces (the fossils and the brush bristles) and water.

a video shows brush being used to pick up tiny ostracode fossils from a dish of sediment

Watch a video to see how a brush is used to pick up tiny ostracode fossils.

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Adhesives and Consolidants
 

Adhesives are an essential part of a fossil preparator's toolkit. We use polyvinyl butyral, a plastic resin, as both an adhesive and a consolidant (hardener). The resin is mixed with acetone, a solvent, in different concentrations depending on the task at hand. Thick solutions are useful for re-joining broken fossils, while a thin solution can be painted or dripped onto fragile specimens, penetrating the cracks and pores in the bone and strengthening the fossil from within, Use of this resin has the benefit of being reversible: a few drops of acetone are usually enough to dissolve any adhesive that was previously applied.

After re-joining the pieces, we often place broken fossils in sand until the adhesive sets. This holds the pieces in the correct positions.

Fragments of a fossil whale skull rest in sand after gluing"

Fragments of this badly broken whale skull have been re-joined and placed in sand, which keeps the pieces in proper alignment as the adhesive sets. Excess adhesive will be cleaned off later. Click to zoom.

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