My Beautiful Laundrette- Preparation With Tensides
Lissy Biber - Bayerische Staatsammlung für Paläontologie und Geologie
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.
How to work with tensides/surfactants:
The tenside used is called Rewoquat W 3690 PG, which is a concentrate of
75% cationic tenside with 24% propylenglycol. It is used for the production
of softeners. It has a pH-value between 4.0-5.5. It can disperse with water.
Tensides work very well on harder sedimentary rocks with clayish or marly
components.
Very often fossils are covered with hard encrustations of marl and clay, esp.
corals, brachiopods and crinoids. The usual way to remove such crusts is by
the use of the airbrasive, which also easily removes details. Tensides work
very well for cleaning, especially on microfossils.
What kind of equipment do I need?
Working with Rewoquat should only be done in a well-ventilated area, if possible in a fume-cupboard; it has a characteristic smell and it can also irritate the eyes. Well-fitting goggles are a must! Rewoquat contains substances which are irritants (Xi R36/38) and degrease skin. Therefore gloves need to be worn whenever handling it. Due to it having 24% alcohol it is flammable and should be stored and handled like any other flammable liquid. Using an air-tight container (eg. Stewart box) prevents any alcohol evaporating. Also needed is a bowl for watering the fossil later on and a brush for removing loosened sediment.
In practice:
The coral I worked on (a heliolites sp. from Gotland) was covered thickly in clay and marl. So to begin with I gave it a careful scrub in water and left it to dry afterwards. The scrub already removed quite a bit of the sediment, but the fossil still covered with a fine layer.
The fossils needs to be dry before putting it into the tenside, otherwise the chemical can not work properly. I then put the coral into a polypropylene box with a well-fitting lid and filled the box with so much Rewoquat until the coral was completely covered.
The fossil is left in Rewoquat for at least 12 hours, because the tenside needs some time to work properly. After 12 hrs you should have a good look, how well it works and how the state of the fossil is. With delicate specimen it is better to take them out after 12hrs and treat them for another 12 hrs rather then leaving them in Rewoquat for too long.
After 19 hrs I removed the coral from the tenside, put it on a wire net and let the tenside drip off the fossil over the container. I then rinsed the coral carefully with water and collected the 1st wash-water. Rewoquat in the concentrated form is pretty harmful for the water-environment even though it is biodegradable, so I always collect the 1st wash-water and put it into the hazardous waste collection.
Replace the washing water with fresh water and leave it there for several hours, until no bubbles appear on the surface (1day). After watering the fossil needs to be left to dry completely again before the next round in the tenside. So leave it overnight to dry properly. Repeat the treatment in Rewoquat and water until all clay and marl sediment is removed.
The sediment falling from the fossil during the process of watering can be sieved and examined for micro-fossils.
After the final treatment in the tenside the fossil needs to be watered very well, otherwise remains from the chemical stick to it. I finally put it into the ultrasound bath (with water) for 5 min, where already loosened sediment is falling from the fossil.
Coming back again to the croco-skull: this is a long time project, because the bone being fragile it needs to be consolidated and so from time to time I have to re-consolidate it again. The problem is finding a good consolidant, because water softens it up.
Fig.2: Heliolites sp. before preparation
Fig.3: after 4 treatments in Rewoquat (219 hrs in total)
Putting my experiences with Rewoquat finally together I can say that the Pros for the use of Rewoquat are:
- It is inexpensive (about 5 Euro/ kg) and it can be reused many times. It just gets cloudier and cloudier each time. If there are too many particles in it, replace it with fresh Rewo.
- It is easy to handle, "preparation while you wait".
- It can be used on extremely detailed, fragile and very problematic fossils. You get very good results, and it leaves no preparation scratches/ marks.
- It is very suitable for cleaning micro-fossils.
- Very good results are received also in combination with other methods, e.g. air-brasive or air-chisels and Rewoquat.
The negative aspects are:
- There is no knowledge about long-term effects; the article by LIERL was published in 1992 and the author has not seen any changes of the treated fossils since then. (The method was mentioned before that in 1985 (Riegraf) and 1990 (Blank) where it was used successfully both times on microfossils from the posidonien-shale (lowerToarcium); also in combination with other methods, e.g. 1st treatment with hydrogen peroxide.
- There are ecological problems even so it is a fabric softener (but highly concentrated): it is forbidden to put any Rewoquat into the water system. It has to go into the hazardous waste collection. Collect the 1st wash-water as well when using Rewo on a larger scale.
- Health and safety precautions you have to deal with.
- So far I could not find a consolidant which is not getting soft in Rewo after 4 treatments (due to the washing water) and so it needs to be put on again. An alternative should be found.
And finally an outlook:
In the latest "Präparator"-magazine there is an article (KRAUS, 2002) about the use of tensides in combination with other chemicals to receive an ideal etching result. They use a combination of 2% or 6% acetic acid, a non-ionic/ anionic tenside and hydrogen peroxide. They also tested several kinds of tensides in combination with various acids and came to the conclusion, that non-ionic and anionic tensides work best. This is definitely worth further investigation.
Supplier for Rewoquat W 3690 PG:
Goldschmidt Rewo GmbH & Co.Kg
Max-Wolff-Str. 7
36396 Steinau
Germany
phone: 0049-6663-54-0
fax: 0049-6663-54-129
References:
BLANK, ? (1990): Tuebinger mikropalaeontologische Mitteilungen.
KRAUS, Werner (2002): ATP Reagenz und Lamipeel .-Der Praeparator 48 (2): Hannover 2002
LIERL, Hans-Juergen (1992): Tenside - ihre Verwendung fuer die Praeparation geologisch - palaeontologischer Objekte.- Der Praeparator 38 (1): 11-17, Bochum 1992
RIEGRAF, W. (1985): Mikrofauna, Biostratigraphie und Fazies im Unteren Toarcium Suedwestdeutschlands und Vergleiche mit benachbarten Gebieten.- Tuebinger mikropalaeontologische Mitteilungen 3 (1): 1 - 210.
Thanks to
Hans-Juergen Lierl for his information over the phone.
Lissy Lange (Biber)
Bayer. Staatssammlung für Paläontologie u. Geologie
Richard-Wagner-Str. 10 80333 München
Germany
email: pal.praeparation@lrz.uni-muenchen.de