Bringing the best out of your fossils: Tips on the preparation of fossils
Byron Blessed (UK)
As many of us know, a good day’s fossil hunting rarely stops when we leave the beach. However, many people do not know what to do with a fossil once they’ve found it. So, here are a few pointers in the art of fossil preparation. This article will not only outline what equipment you will need but will also give you general guidelines on how to use it.
The first thing that any fossil preparator needs (and it isn’t something you can buy) is a lot of patience. The second thing you need is … a lot of patience! This cannot be stressed enough. Fossil preparation is a long, sometimes boring and laborious process and it is all too easy to damage specimens by being too hasty!
It must also be noted that fossil preparation is not something that can easily and successfully be taken up overnight. Most of the best preparators have been in the business for decades. To think that you can immediately match their skills over night is naïve to say the least. Like any good hobby or job, practice makes perfect. In addition, it can be very costly to get all the right kit so this can become an expensive hobby.
Washing specimens under the tap is a good, first step and will reveal hidden detail by removing unwanted mud and sand. Many clays and muds can be removed this way particularly with the help of an old toothbrush and a scalpel.
However, care must be taken, as many mudstones, siltstones and shales do not like water being put on them and have a tendency to disintegrate, craze or crack when dried out. To stop this, a stabilisation process must be undertaken by running superglue in between cracks to consolidate the matrix and resins can be used to reinforce the fossils themselves.
Harder, calcareous nodules and pebbles (like those found on the Yorkshire and Dorset coasts) can only be prepared by using some kind of pneumatic tool to remove unwanted rock. Many amateurs use engravers, dremmel tools and so on.
However, these are not designed for a heavy workload (for example, on iron pyrite encrusted rock) as can soon be seen when their fragile motors burn out. Also, these types of tools generally have a rotating tool head that is totally unsuitable for preparing fossils.
Rather, one needs a tool that will “chisel” the rock and, therefore, a tool head that moves up and down is needed. The best tools for this job (and the ones that all the top, fossil preparators use) are the Chicago Pneumatic and Aro Airscribe “Pens”. These pens vibrate a tungsten carbide tip using a supply of compressed air. Generally, these pens have to be slightly refitted for fossil preparation work (the pistons need reinforcing).
There are several types of these pen that can be used:
- The Aro pen. This is ideal for beginners and for softer and smaller items.
- The CP (Chicago Pneumatic with refit). This is used by the more experienced users as it can be used for a multitude of tasks. (It is the pen I always use – my weapon of choice!)
- The Needle CP. This is for use on extremely delicate fossils such as trilobites.
- The CP Chisel Model. This is for taking matrix off quickly but with additionally benefits (see below).
Note that, when using these tools, large volumes of rock and dust are produced. Therefore, adequate ventilation, heavyduty dust masks and eye protection must be used at all times.
The best way to use these tools is to gently tease, scrape and chisel at the rock to remove it. Sometimes, a grain-by-grain approach must be undertaken. For example, centres of ammonites can be very difficult to prepare. As you slowly remove each layer of rock, you should also think about how you intend to display the piece. That is, you should have regard to its overall appearance. I always have a picture in my head of what the final piece should look like.
Getting a nice smooth finish to the surrounding matrix is difficult and can take longer than extracting the fossil itself. Grinding tools can be used but an expert can use the CP pen to greater effect. To accomplish a smooth finish, I use a “colouring in” stroke to my pen work. This “colours” the rough area with a smooth surface. Remember – practice is needed when using this technique.
Once smoothed, an air abrasive machine (mini-sandblaster) can be used to remove the last layers of matrix. These machines also run from compressed air. The compressed air is combined with a fine medium of powder (usually aluminium oxide or baking powder) and is blown out of the nozzle. This is a very effective means of preparing soft matrix fossils such as crinoids and trilobites or, indeed, other fossils where vibrating tools would be too aggressive. Unfortunately, only a professional preparatory will tend have this kind of expensive kit.
The final stage in the preparation process is the protection of the fossil. The best way to do this is to coat your fossil with a protective layer of varnish and seal it from the outside world. This is a touchy subject with many collectors, academics and fossil preparators.
The main problem is that whatever you use could unintentionally damage the fossil and may also hide all the fine details that could be used in the identification process. Therefore, never use heavy varnishes such as yacht varnish. Always use something that is water-soluble or can be removed with white spirit. I use a weak artists’ varnish that is soluble in white spirit and can be removed with an air abrasive. Never use oil-based varnishes, PVA glues, boot polish or resins.
The use of chemicals is generally to be avoided. Various nasty acids can be used to remove mainly vertebrate material from within limestone pebbles. However, only professionals should really attempt this because of the dangerous nature of some of the acids used.
Hopefully, this article has given you a “beginners’ guide” to the world of fossil preparation and, hopefully, it has also given you a greater appreciation of the amount of time, patience, blood, sweat and tears that goes into producing a fabulously prepared fossil (hence the price of professionally prepared examples). But don’t let that discourage you.
The pictures accompanying this article show a few examples of what can be accomplished by using the techniques outlined above. Please visit my website, Fossils-uk more information.