The beaches at Charmouth are full of a whole range of different fossils for both beginner and expert fossil hunters to find and enjoy, but what should be done with them once they’ve been discovered? Many of the fossils from the beaches here are loose in amongst the shingle, already washed out from the surrounding rocks and in need of no more preparation than some washing or sitting in fresh water to extract any remaining sea water. For those fossils still in a block of limestone, sometimes splitting the rock with a geological hammer is all that is needed to reveal some incredible finds, in other cases a bit more work may be required to display the fossil’s full potential.
Fossil preparation is primarily concerned with best displaying your fossil finds and can be an incredibly satisfying part of enjoying palaeontology as a hobby or profession. There are many different preparation techniques available to fossil collectors but not all of these will be suitable for all cases, which technique you use is heavily dependant on the type of fossil you’re considering working on. The fossils on display around the Centre are prime examples of the different techniques that can be used to best showcase the fossil. Depending on your level of investment and the amount of material you’re working with, fossil preparation can be as expensive or inexpensive a part of the hobby as you wish, particularly if you’re thinking of just getting started.
Fossil polishing is a cost-effective means of preparing fossils, in particular fossils such as ammonites on the tops of pebbles or fossils that have been cut or split in half. It’s simple to do and can produce some fantastic looking results, all that is needed is several grades of sandpaper and some varnish, clear nail varnish is suitable to use and perfect if you only have a couple of fossils that you would like to work on.
Polishing the fossil is a simple job, working from coarser grained sandpaper (40-80 grade) to finer grains (120-180 grade). Whilst sanding down the surface with the fossil on remember to use a circular motion to ensure an evenly smooth surface. The rocks from Charmouth can be quite soft and sanding them down shouldn’t take long. Once your fossil has been polished down to a level you like rinse the fossil off and allow to dry, once dry apply an even coating of varnish to the rock, a quick coating of clear nail varnish is often enough for many finds. This will both protect the fossil and should enhance the contrast between the rock and fossil while highlighting details.
Warning: While sanding down a fossil it is important to dampen it first to avoid generating rock dust which may be harmful or inflame respiratory conditions. You may wish to wear a dust mask for this.
If you wish to try out fossil polishing for yourself but haven’t found a suitable fossil, fossil polishing kits including two ammonites and all the materials you need are available in our shop at the Centre.
Air Pens & Air Abrasives
Air pens and air abrasives are generally the go to tools for fossil preparation for professional preparators, many of the fossils on display around the Centre have been worked on using these tools. Air pens are effectively handheld pneumatic jackhammers, these tools have a metal tip that moves up and down at very high frequencies, hitting the rock thousands of times a minute, shocking off bits of rock as it goes. These come in a variety of sizes depending on how much rock the preparator is looking to remove with larger air pens being used to remove bulk material and much finer tools for detailed work.
Air abrasives are tools that spray fine powders at the rock, shocking the material to remove rock. This is typically done for finer scale work and in the finishing stages for an area being prepared. The powders used can be changed depending on the material being worked on, the ideal is using a powder that is harder than the rock being removed but softer than the fossil itself to prevent damaging it. A variety of powders can be used by these tools such as sodium bicarbonate, dolomite or iron powder.
Both air pens and air abrasives require a specialist set up, space and can be very expensive to purchase everything, run and maintain. These tools require a lot of patience and skill to use properly as one wrong move could mean the fossil being worked on getting damaged. While not necessarily cost effective or suitable for a couple of prized ammonites found on one of our fossil hunting walks there are cheaper alternatives available in a modified dremel.
Tools that have still been used since the earliest days of fossil preparation do still have a place in modern usage. For precision and extremely delicate material hammers and pins can still provide excellent control in removing rock and the outer layers of shell, particularly on the centres of ammonites which can be notoriously difficult to approach for beginners. Lightweight hammers, carbide needles and even scrapers like those used in dentistry can all be used to great effect for trickier jobs.
Modified dremels provide a fantastic opportunity to get into fossil preparation for those interested in it. These tools are perfect for starting out costing approximately £50 and running off of just electricity without the need to invest potentially hundreds in air compressors and the other necessary elements to using an air pen or abrasive. These dremels should be modified so that the tips oscillate up and down, similar to an air pen, rather than rotating and should be fitted with tungsten carbide tips.
Note: Tungsten carbide tips are used as these are more resistant to breaking while working rock, a regular dremel tip will break when working rock.
These tools, while less refined than an air pen, can still provide fantastic results with some practise and patience. It is always advisable to work on something other than a prize find first, the tool can take getting used to and understanding how the rock will behave is important. Each different kind of rock will break in different kinds so it is always best to practise with material as similar as possible. It is important to work slowly and carefully, especially when approaching the fossil, it is always useful to keep some adhesive close to hand in case any of the fossil does chip away. These tools can be quite loud and vibrate a lot so if used for long periods of time ear defenders and vibration resistant gloves may be useful, taking breaks often is advised.
Warning: Caution must be taken when using a dremel, air pen or air abrasive. Rock dust can be harmful, especially silica rich rocks like those from Charmouth and so a medical dust mask should be worn(grade FFP3 or N99 as a minimum). Eye protection should be worn as chips of rock will go flying. Using these tools is not suitable for children as the vibrations may result in damage to developing hands and wrists.
Various chemicals can also be used in fossil preparation, however these techniques are strictly recommended for people familiar with fossil preparation and handling chemicals. Many of these chemicals are hazardous and so must be used in a controlled way both to protect the fossil and the user. If used properly they can produce stunning results but the process can be very slow and is only viable for some fossils.
Acetic acid is sometimes used to react away surrounding rock from the fossil, eroding away carbonate material and potentially the fossils too if due diligence is not taken. The process involves coating the fossil in protective resin and then placing the rock in acetic acid at the right concentration (around the same concentration as the vinegar that goes on chips) and leaving it to react for about a day, then transferring it into water for twice as long in order to wash off excess acid. This will take approximately 1mm of thickness from the rock while the resin will protect the fossil from the acid. This process is repeated with fresh coatings of resin as more and more of the fossil has been revealed, caution is always taken to ensure the strength of the acid is correct so as not to react too quickly and destroy the fossil. This is viable for things like bones however calcite fossils, like many ammonites, are not suitable for acid preparation. It can sometimes take several months of repeating these processes to reach a satisfying conclusion.
In many cases, depending on the type of fossil being worked on, acids are not suitable. Other chemicals can be used to break down the rock around the fossil but many of these chemicals pose a significant health when used improperly and should only be used by experienced preparators. Such chemicals are used once as much of the rock has been removed mechanically with a dremel or an air pen. The chemicals are applied to the remaining rock on the fossil and left to react. After several hours (and regular monitoring) the chemicals are scrubbed off of the fossil and left in water for several days to a week in order to draw out as much excess as possible. Any remaining chemicals will continue to react and may damage the fossil.
Surfactants can work in a similar way, being the same chemical present in detergents they are able to bind to clay molecules in the rock. This causes the clay molecules to swell and break apart from each other at which point they can be scrubbed away. This technique is particularly good with calcitic fossils which won’t react with the surfactants but other types of fossils may be destroyed by the process.
Warning: These techniques are only used in situations where mechanical preparation is not viable and should not be used by those unfamiliar with them. Extreme care must be taken whenever handling chemicals for fossil preparation. Those interested in chemical preparation should seek advice in advance.
Zoic Palaeotech sell many of the tools suitable for preparing fossils found on our beach and offer in depth information on how to best use the equipment safely
The Fossil Academy is run by Dan Brownley, former warden and one of the local private walks operators who also does fossil preparation guide videos on his Youtube channel