How to prepare fossils

There are a vast range of options when preparing a fossil, depending on how the item is preserved and in what type of matrix it is in. All preparation methods will use the differences between the matrix and the fossil as the basis for preparation.

The most common way is mechanical preparation using hand tools or compressed air powered tools (such as air scribes or air abrasives (sandblasting). These methods exploit a difference in hardness between the fossil and the matrix or a line of weakness between the fossil and the matrix.

Alternatively, we can use chemical methods to prepare the fossil where the chemicals are used to either dissolve or disintegrate the rock around the fossil. Depending on the matrix and fossil preservation it is possible to use acids, alkalis and even surfactants to reveal fossils where mechanical preparation may not be possible. Which chemical you use depends entirely on the rock type and the composition of the fossil - if they are the same composition then chemical preparation is not going to be an option! 

The first decision for any preparator concerns how much work is needed on a specimen.  Any intervention is going to affect the fossil in some way, so the initial question must always be "What is going to happen to the fossil after preparation?" If it is not going to be researched immediately, often the best course of action is to remove excess matrix (to save storage space) and then if needed just conserve the fossil so it will not deteriorate in storage. The minimum of intervention is always the best as this reduces any potential risk to the fossil and the information the encasing sediment holds. Sometimes the best course of action may just be conservation particularly if the fossil is fragile or very small.

Today it is perfectly possible to use CT scans to digitally “excavate” a fossil. This method was used by Elsa Panciroli of Oxford University to reconstruct an early “mammal” called Borealestes from Scotland. The fossil was in a hard matrix block about the size of an apple so there was little to no preparation needed as the CT scan was able to identify each of the bones in the block and allowed Elsa to put them back together digitally into a fully articulated skeleton.

If the fossil is going to be researched or needs to be further prepared just to reveal what it is, then we need to understand “what do we need to see” to study the fossil. This will then prompt questions about how to remove matrix, how to ensure we protect the fossil during preparation, and perhaps most importantly understand what risks or sacrifices are going to be needed in order to expose the fossil. This decision is very important because removing matrix will always remove information such as stratigraphical, depositional, palaeoenvironmental, and palaeoecological data including trace fossils such as skin impressions. Therefore, deciding how much information to remove in order to see a fossil has no standard answer; the question itself, however, is intrinsic to every matrix removal task. If the fossil is destined for display in the museum, then this will complicate any decision making because we often want more of the specimen revealed than is strictly necessary for research purposes which will then add additional risk to the preparation process.

Preparing dinosaur fossils is a privilege because you are the first person to see the specimen revealed from the matrix.  You have a duty to ensure you treat the fossil with maximum respect and care to ensure it is properly preserved and prepared with the minimum of damage. This approach followed with appropriate storage will result in the long-term safeguarding of the collection.  Working on any specimen is always a series of decisions and risk assessments but there is never a “textbook” answer available to solve any problem!