Cleaning shell fossils can be a delicate, pain-staking process. The time and tools required depends on the type and size of fossil and the surrounding matrix. You don’t necessarily need special tools for the job, but sometimes they can be a huge time saver and greatly increase the quality of the end product.
If you have found a cluster of shells in a very hard matrix, the best course of action may very well be to leave it as it is. Trying to release the fossils from the matrix may cause more damage than reveal treasures. But for single specimens that are larger or spaced apart, there are a number steps that can be taken to reveal hidden details and prepare them for display.
How To Clean Shell Fossils
Follow the tips below to learn how to clean sea shell fossils.
1. Hardening Soft Specimens
Some fossils may be so fragile that a gentle brushing will be all you can do to prevent damage. These types of specimens may benefit from a hardening solution.
This is especially true of delicate fossils in a soft shale matrix. Never apply water to this type of specimen. The shale will absorb water and either explode or disintegrate, often taking the fossils with it.
Hardening agents can be applied to make fragile specimens more stable. If you have a fossil in a shale matrix, you may apply hardener to the entire piece or just soak the underside to stabilize the shale. Many of the chemicals suggested to make a hardening solution are irritants or flammable. Use these ingredients outside or in a well-ventilated area, and wear appropriate eye and face protection.
You can make a hardener from the following ingredients:
- 2-5 tablespoons flake-form polyvinyl acetate or cellulose acetate in sheets or flakes
- 1 pint toluene or acetone
- Dissolve for a day or so
- Store in well-sealed jar
Instead of the above recipe, you can dissolve fresh Duco cement in a few spoonfuls of toluene or acetone for small jobs. Brush your choice of prepared hardening mixture on the specimen, or immerse for a few seconds. Dry for 5-10 minutes in a well-ventilated area.
If you think the result is too shiny and the fossil will stand up to it, you can wipe it down with a cloth soaked in fingernail polish (acetone). Try a small area first or use a less desirable specimen to experiment with the whole process.
2. Cleaning Shell Fossil Specimens
Most specimens can be washed in water with a very small amount of detergent. An old toothbrush is a great tool for removing dirt and other debris. Rinse the specimen in clean water and allow it to dry thoroughly before proceeding.
3. Removing Excess Matrix
The hardness of the matrix and the type of fossil determine how much matrix should be removed. You may want to leave some matrix material to support the fossil for display. Again, experimenting with less impressive or less important fossils will help determine the best procedure.
One popular way of removing matrix is to soak the specimen in a 50/50 solution of vinegar water for about an hour. For some specimens a weaker solution may be a better choice.
After an hour, remove the specimen and detach any dissolved matrix. Examine the specimen for any damage. If the fossil is in good shape, the soaking procedure may be repeated several times until the desired amount of matrix has been removed.
After soaking, specimens can be washed with a bacterial soap solution if desired. Rinse thoroughly in fresh water and allow to dry in a cool, darkened area. Avoid direct sunlight on fossils that have been buried for millennia in the dark earth.
Excess matrix can also be removed with pliers, a hammer, or a saw. Be careful that the specimen is not being affected by these rough methods. As you come closer to the fossil, continue to remove matrix using short, careful strokes with an awl, nail, or hobby knife.
Here’s where a mechanical tool comes in handy, such as a Dremel, dental drill, or some type of small pneumatic pen-type tool. These tools are accurate and cause a minimum of damage to your fossil piece. These types of tools are featured in YouTube fossil prep videos and it’s easy to see why they’re highly recommended.
4. Filling Cracks/Repairing Damage
Fossils can be repaired with many different types of glues and fillers. Broken pieces can be joined with simple white craft glue or super glue. Damage can be repaired with Plaster of Paris. Or colors can be matched with a mixture of cement pigment added to the Plaster of Paris, water putty, or epoxy.
You may want to do a bit more research in this area, as there are many websites and forums with a plethora of opinions about what will work best. There are also some who would not recommend any repair work be done to a natural specimen.
5. Preserving the Specimen
Here again, there are a multitude of ideas and opinions from sources with various degrees of experience. Purists will balk at any type of preservative coating. But many professional paleontologists do use them in order to present a more appealing and durable display.
Before adding any coating, make sure your fossil has had time to dry completely. Otherwise, the coating may become foggy or the fossil may become damaged by mold from trapped moisture.
If you are preparing a hard, pyritized specimen, lightly brushing the surface with a soft brass brush can increase the fossil/matrix contrast and bring out a kind of metallic luster. However, that luster may come at the expense of some fine details of the piece.
To increase contrast, you may try a very thin coat of non-glossy finish, such as an acrylic spray, yellow dextrin, paste wax, petroleum jelly, slate dressing, or even sun screen. Thick coatings of varnish, paint, or plastic-based coatings are not recommended. And don’t forget to label your specimen once preparation is complete.
To Bleach or Not to Bleach
For the most part, bleach is not a good idea for cleaning and preserving fossils. The one exception I’ve read about is fossils collected from petroleum-rich shale or soil. These fossils may be oil-stained, and a weak bleach or gasoline solution may be the answer to removing those petroleum stains. Experiment on small or unimportant specimens before trying bleach on a major find.