Fossil Preparation

Fossils are in most cases discovered in the rock, recovered therein and then require professional preparation to be exposed. Only then can the fossils be examined, studied or simply viewed and admired. The preparation of fossils requires skill, experience and many different tools and aids. Since each fossil is unique, safe and adequate use of these tools is most important. Such a wealth of experience for fossil preparation must be built up over many years and constantly expanded. 

Tools

In mechanical fossil preparation, the fossils are exposed by hand with the aid of various tools. The most important of these are pneumatically operated preparation chisels, which are small “jackhammers” that can precisely remove rock. In addition, there are preparation needles, scalpels, chisels, brushes and paintbrushes. Grinders or “multi-tools” are also very useful, as various attachments can be used for grinding, drilling or milling. Fine sandblasting equipment, like pneumatic chisels, is of particular importance. By using different air abrasives, both hard and soft rocks can be processed. The advantage lies in the almost vibration-free nature of rock removal. This is a great advantage over chisels, especially when exposing spines or other delicate fossil parts. By using different nozzles with different diameters, mostly in the range of 0.4 – 1mm, even the smallest details can be prepared with a lot of practice.
For the use of air-powered tools, an air compressor, cabins and an exhaust system are mandatory. In order to achieve really good results, especially in fine preparation, the use of a binocular with at least 10x, but better at least 20x magnification is obligatory.

Air abrasive for fine preparation of fossils
Preparation of a trilobite with a pneumatic chisel

Chemical Preparation

Chemical preparation involves the use of chemicals to expose the fossil substance. Most commonly, acids such as acetic acid, formic acid, or hydrochloric acid are used in highly dilute concentrations to prepare silicified fossils from limestone. Fossils in marly or oolitic rocks can be prepared with alkalis, e.g., potassium hydroxide or even surfactants, e.g., rewoquat (can be diluted with alcohol). When using such chemicals, it is essential to follow the manufacturer’s safety instructions, to wear gloves and protective goggles, and to ensure adequate ventilation.
The use of chemical preparation techniques should be carefully considered depending on the individual case. For example, some fossils can be satisfactorily prepared almost exclusively with acids, whereas most other fossils would probably be destroyed. In my experience, mechanical preparation is preferable as long as very good results can be achieved and the time required remain reasonable.

Keichousaurus prepared with formic acid

Bonding, securing and consolidating

Since most fossils are recovered from the surrounding rock using a hammer and chisel, damage often occurs. In most cases, the fossils have to be reassembled from two or more individual parts, or at least cracks have to be filled. Superglues, epoxy resins or 2-component adhesives in various viscosities are usually used for this purpose. Depending on taste and the goal of the preparation, emphasis can be placed on authenticity or a show effect, e.g. by coloring or not coloring the adhesive. With a lot of practice, it is possible to make some adhesions “disappear” or to make them visible only at second glance.
Whether due to weathering or stress during recovery, the substance of some fossils is shocked, fragile and sensitive and requires strengthening. Superglue can also be used for this purpose. In many cases, however, products that are soluble in acetone, such as Mowilith or Paraloid, are more suitable.

Predatory fish from the Plattenkalk broken into 15 pieces
The same fish after gluing, preparation and matrix design.

Restoration and Reconstruction

In most cases, fossils are not completely or perfectly preserved. Depending on your wishes, damaged sections can be restored and missing parts reconstructed. What exactly and how much should be restored is often a difficult decision. With some experience, it is much easier to weigh possible restoration options against each other.
As a rule, restoration work is done with epoxy resin, which can be colored as desired. Reconstruction of e.g. spines in trilobites requires some practice and skill, but can make a big difference in the overall effect of the specimen.

Illaenus with heavily weathered cephalon
Illaenus with restored cephalon

Last but not least: the design

Since elaborately prepared fossils are usually exhibited as collection items in the showcases of fossil enthusiasts or also in museums, the design of the specimens is of importance that should not be underestimated. Even before preparation, it is therefore important to plan how the specimen should look in the end. Similar to the topic of restoration/reconstruction, many things are possible, from the most natural and unobtrusive to the most dramatic presentation. In addition to craftsmanship, this requires above all an aesthetic sensibility and a philosophy of one’s own as to what the preparations should ultimately express. In maximizing the show effect, in my opinion, the natural character of the fossil and the stone should always be in the foreground in order to offer an authentic look into the past.

This heteromorphic ammonite was prepared in a way, so that the round shape of the fossil contrasts harmoniously with the smoothed geode.

Case study Minicryphaeus:

I wrote a detailed article on the preparation of a Minicryphaeus giganteus from the Devonian of Morocco, in which I go into all the steps from checking the unprepared fossil to the finish. This article allows you to follow the whole preparation process. (Click the picture to get to the article, alternatively here: https://www.steinkern.de/english-articles/1328-minicryphaeus-english.html)