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Non-destructive, safe removal of conductive metal coatings from fossils: a new solution

David Jones, Jennifer Hartley, Gero Frisch, Mark Purnell, and Laurent Darras

Plain Language Abstract

Scanning electron microscopy is an important technique for making images in the sciences and often requires that the specimens to be imaged are coated with a thin layer of metal, such as gold, platinum or silver. However, the application of such metal coatings changes the appearance of specimens and can obscure important features, and thus may be undesirable, or even prohibited by those who look after the specimens. We describe a harmless, straightforward and inexpensive technique for removing gold coatings for specimens. The method involves immersing samples in liquids that react only with the metal coating. No further handling is needed, no poisonous substances are used in the process and the liquids can be tailored to remove other metal coatings.

Resumen en Español

Una nueva solución para la eliminación segura y no destructiva de recubrimientos de metales conductores en los fósiles

La microscopía electrónica de barrido y otras técnicas de generación de imágenes requieren habitualmente que los ejemplares analizados sean recubiertos por un metal conductor tal como oro, oro-paladio, platino o plata. Sin embargo, la aplicación de recubrimientos metálicos cambia la apariencia de los ejemplares y puede ocultar características importantes, lo que la convierte en un método no recomendable o incluso prohibido por instituciones y conservadores. En este artículo describimos una técnica inocua, sencilla y económica para eliminar el oro. El método consiste en la inmersión de las muestras en líquidos iónicos y su posterior aclarado con agua. No se necesitan más tratamientos ni se utilizan compuestos tóxicos en el proceso, y los líquidos pueden adaptarse para eliminar otros recubrimientos metálicos sin que se vea afectado el adhesivo usado para fijar el ejemplar en el soporte.

PALABRAS CLAVE: microfósil; recubrimiento metálico; SEM; líquidos iónicos

Traducción: Miguel Company

Résumé en Français

Nettoyage non destructif des revêtements métalliques conductif sur les fossiles: une nouvelle solution.

La microscopie électronique à balayage ainsi que d'autres techniques d'imagerie demandent souvent que les spécimens soit enduits d'un métal conductif, comme l'or, l'or-palladium, le platine ou l'argent. Cependant l'enduction des spécimens change leur apparence et peut cacher des caractères important. De fait elle est parfois non désirée voire même interdite par les conservateurs ou les institutions. Nous présentons une technique simple, peu onéreuse et non-destructrice pour enelver l'or. Cette méthode demande d'immerger les échantillons dans des liquides ioniques et de les rincer à l'eau. Aucune autre intervention n'est nécessaire, aucun composant dangereux n'est utilisé dans ce procédé et les liquides peuvent être modifiés pour enlever d'autres types d'enductions métalliques sans affecter l'adhésif utilisé pour maintenir le spécimen sur son substrat.

Mots-cléfs: microfossile, enduction métallique, SEM, liquides ioniques.

Translator: Loïc Costeur

Deutsche Zusammenfassung

Zerstörungsfreies, sicheres Entfernen von leitenden Metallüberzügen bei Fossilien: Eine neue Lösung

Rasterelektronenmikroskopie und andere Abbildungstechniken setzen normalerweise voraus, dass die abzubildenden Stücke mit einem leitenden Metall wie Gold, Gold-Palladium, Platin oder Silber beschichtet werden. Ein solcher Überzug ändert jedoch das Erscheinungsbild der Stücke, da auf diese Weise wichtige Merkmale verdeckt werden können. Daher ist eine Beschichtung nicht wünschenswert oder wird möglicherweise sogar von einigen Museen und Kuratoren verboten. Wir beschreiben eine harmlose, einfache und kostengünstige Technik, wie das Gold entfernt werden kann. Die Methode erfordert lediglich, die Proben in ionische Flüssigkeiten einzutauchen und mit Wasser abzuspülen. Es ist keine weitere Behandlung nötig, es werden keine giftigen Verbindungen benutzt und die Flüssigkeiten können auf die Entfernung anderer Metallschichten angepasst werden ohne sich auf das Klebemittel auszuwirken mit dem das Stück am Trägermaterial befestigt ist.

SCHLÜSSLWÖRTER: Mikrofossil; Metallüberzug, SEM; ionische Flüssigkeiten

Translators: Eva Gebauer and Anke Konietzka

Arabic

303 arab

Translator: Ashraf M.T. Elewa

Polski Abstrakt

Niedestruktywne i bezpieczne usuwanie przewodzących powłok metalowych z skamieniałości: nowe rozwiązanie

Elektronowa mikroskopia skaningowa, a niektóre inne techniki obrazowania, często wymagają, by fotografowane okazy były pokryte metalem przewodzącym; np. złotem, złotem-palladem, platyną lub srebrem. Jednak zastosowanie powłok metalowych może być niepożądane, a nawet zabronione przez instytucje lub kuratorów, ponieważ zmienia wygląd okazów i może przesłaniać ważne cechy. W niniejszej pracy opisujemy nieszkodliwą, bezpośrednią i tanią technikę stosowalną w celu usuwania złota. Metoda polega na zanurzeniu próbki w cieczy jonowej i wypłukaniu w wodzie. Żadna dodatkowa manipulacja nie jest potrzebna, żadne trujące związki nie są w tym procesie wykorzystywane, a ciecze mogą być dostosowane do usunięcia innych powłok metalowych nie wpływając na spoiwo użyte do przymocowania próbki do podłoża.

Słowa kluczowe: mikroskamieniałość, nakładanie powłok metalowych, elektronowy mikroskop skaningowy, ciecze jonowe

Translators: Dawid Mazurek, Robert Bronowicz, and Daniel Madzia

Anke Konietzka
 

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David JonesSchool of Earth Sciences
University of Bristol
Wills Memorial Building
Queen's Road, Bristol
BS8 1RJ, United Kingdom

David Jones is a Visiting Fellow at the School of Earth Sciences, University of Bristol. He completed a Ph.D. on conodont palaeobiology at the Department of Geology, University of Leicester.

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JenniferHartleyDepartment of Chemistry
University of Leicester
Leicester, LE1 7RH
United Kingdom

Jennifer Hartley is a Ph.D. student in the Chemistry Department at the University of Leicester. She is researching novel methods of metal recycling using Deep Eutectic Solvents with a special focus on environmentally responsible techniques. Her project is funded by the EPSRC and MCP Ltd. Jennifer completed her MChem Chemistry degree at the University of Leicester in 2009.

 

 

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Gero FrischDepartment of Chemistry
University of Leicester
Leicester, LE1 7RH
United Kingdom

Gero Frisch is a Teaching and Research Fellow in the Chemistry Department at the University of Leicester. He received a PhD degree from the University of Freiburg, Germany, in 2006. With his research in ionometallurgy he explores the link between speciation and chemical behaviour of metal ions in ionic solvents. He uses a combination of spectroscopy and electrochemistry in order to find efficient metal processing techniques.

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Mark PurnellDepartment of Geology
University of Leicester
Leicester, LE1 7RH
United Kingdom

Mark Purnell’s research interests range across functional morphology, palaeobiology, taphonomy, palaeoecology and taxonomy, with a current focus on taphonomic biases arising from decay and preservation of soft tissue characters, and the use of 3D microtextural analysis of tooth wear for dietary discrimination in vertebrates. He did his PhD at the University of Newcastle upon Tyne on the taxonomy, palaeoecology and biostratigraphy of conodonts from northern Britain, and after postdoctoral work in Toronto, came to Leicester, where he has been ever since.

 

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Department of Geology
Laurent DarrasUniversity of Leicester
Leicester, LE1 7RH
United Kingdom

Hailing from the old privateer town of Dunkerque (where the only palaeontology to do is telling fishermen the difference between a whale's rib and a mammoth's tusk) Laurent Darras started studying palaeontology at the University of Lille 1, under the supervision of Prof. Alain Blieck hand-picking conodonts and brachiopod shells from Ordovician sediments, then discovering the world of jawed vertebrates with fossils of mostly placoderms from the Devonian of the Boulonnais. Now he is finishing a Ph.D about the macro-ecological consequences of grazing and shell-crushing in fishes, while also investigating aspects of the palaeo-ecology of early gnathostomes, all of that under the supervision of Prof. Mark Purnell at the University of Leicester.

 

APPENDIX

The following recipe summarises the method for producing a standard quantity of the iodine solution:
To make ca. 1000 cm3 of Ethaline, mix 590 g of choline chloride and 530 g of ethylene glycol stirring at ca. 60°C until a clear homogenous liquid is formed.

Ethaline is stable and can be stored in glass or plastic containers for prolonged periods.

To make 100 cm3 of 0.02 mol dm-3 iodine solution for gold removal, add 0.5 g of I2 to 100 cm3 of Ethaline, stirring at ca. 60°C.

The iodine solution can be stored in a glass container for a week.

 

FIGURE 1. Optical images showing visual appearance of microfossils and micro-vertebrate remains before gold coating and after gold removal. 1, 2, Conodont element, Wurmiella excavata, Tramway Netherton, UK, Silurian: 1 before gold coating, 2 after removal. 3, 4, Sarcopterygian scale (probably Onychodus), Gogo Formation, Devonian, Australia: 3 before gold coating, 4 after removal. 5, 6, extant foraminiferan Globorotalia menardii (Caribbean Sea, 2900m water depth): 5 before gold coating, 6 after removal. 7, 8, Fragment of dermal armour, probably heterostracan, Devonian, Welsh Borders, UK, 7 before gold coating, 8 after removal. Scale bar equals 500µm.

figure1

FIGURE 2. Scanning electron micrographs showing fine-scale surface textures of fossil microvertebrate remains before gold coating and after removal. 1-3, Sarcopterygian scale (probably Onychodus), Gogo Formation, Devonian, Australia: 2 before gold coating, 3 after removal (same specimen as Fig. 1.3,4). 4-6, Fragment of dermal armour, probably heterostracan (bony surface), Devonian, Welsh Borders, UK: 5 before gold coating, 6 after removal. 7-9, Fragment of dermal armour, probably heterostracan (dentine surface), Devonian, Welsh Borders, UK: 8 before gold coating, 9 after removal. 10-12, Sarcopterygian lepidotrichia (probably Onychodus), Gogo Formation, Devonian, Australia: 11 before gold coating, 12 after removal. White boxes in low-magnification images show location of high-magnification images. Low magnification scale bar equals 500 µm. Field of view of high-magnification images is 50µm.

figure2