My Beautiful Laundrette- Preparation With Tensides

In my talk "my beautiful laundrette - preparation with tensides" I want to introduce you to an interesting way of chemical preparation.

Several months ago I was given a specimen for preparation, which gave me quite a bit of a head-ache. The object is a crocodile-skull (the size of a lemon) from a middle Jurassic fossil site in Germany which is covered by an extremely hard kind of clay-sediment. Trying to prepare it mechanically proved to be extremely difficult, if not saying impossible, the sediment being rock solid and the fossil structures being very delicate. The air-brasive failed as well. Chemical preparation with NaOH-Chips (often used on this material) did not work, acid I wanted to avoid because of the skull being so delicate.

Doing some research to find a solution I came across an article in the magazine "der Praeparator" , the organ of the german preparators organization, which was very interesting. It was an article called "tensides- their use in the preparation of geological- palaeontological objects", written by Hans-Jürgen Lierl (1992). It was about how fossils embedded in clay and marl or rocks with clay and marl components can be prepared with tensides. The method described sounded so easy and effective, that I tried it immediately. In this talk I want to give an account of my experiences with this method and show you some results.

What are tensides?
Tensides/ surfactants are soaps or soap-like substances with special properties. They are used for a long time now for washing and cleaning purposes. Nowadays they are produced synthetically.

How do they work?
To make it brief: Tensides work on solid/liquid interfaces, because their molecules having a hydrophilic (that is water-loving) and a hydrophobic part (water-repellent). Dirt-particles are enclosed by the hydrophobic part, the hydrophilic part reduces the tension at the water surface. The dirt cover is breaking apart into small pieces, dispersed, lifted up and washed away.

The exact chemical and physical processes going on when using it on fossils are still not totally clear, but it is thought that the cationic properties cause a reduction of the surface tension of water and therefore the tenside can work in the smallest pores and cracks of the sediment.

After reading the article I tried it on the crocodile-skull and it seemed to work, but the process being very slow. I wanted to try this method on more suitable fossils.
Fortunately two of our scientists came back from Gotland/ Sweden, where they collected beautiful corals. They are of Silurian age (~430 mio. years) and encrusted in marly clay- the perfect sediment due to the article.