Foil removal

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Foil copy of a hematite reef rubble, Elbingeröder complex , Harz
Foil print of a zebra lime, Rübeland
Foil print of a Dismikrit , Elbingerode
Foil copy of a Neptunian Ganges , Rübeland

The production of foil prints is a preparation technique in sedimentology for the documentation of ground, polished and etched surfaces of rocks , whereby the surface structure is transferred to suitable foils with the help of solvents , mostly acetone .

preparation

The rock to be examined is first sawn and ground with abrasive powder , mostly silicon carbide , with a coarse grain size F28 (600 µm). For greater detail, the surface can be smoothed with aluminum oxide (grain size 1 µm). The surfaces of carbonate rocks prepared in this way can be etched with acetic acid , formic acid or hydrochloric acid so that a micro-relief is created. The prepared sample is carefully washed and dried. For the quality of the print, it is crucial that the surface is no longer touched after etching and that it is completely level in a sandbox or with modeling clay so that the surface can be completely wetted with solvent . After wetting, the film is rolled onto the surface as quickly as possible before the solvent evaporates , free of dust and bubbles, and after approx. 5–10 minutes turned over to dry on the film side and allowed to dry for a few days. Then the film can be carefully peeled off the rock, cut to the edges and pressed between glass plates.

solvent

As solvents for carbonate rocks, methyl acetate , ethyl acetate , ethyl lactate , 1,1,2,2-tetrachloroethane and acetone can be used, whereby in practice the use of acetone has become established. For silicate rocks, etching the surface with 30% hydrofluoric acid has proven itself.

Foils

First attempts to represent replicas of rock surfaces were made in 1968 with the help of trichlorethylene and ethyl cellulose . However, these prints were very fragile and also of different thicknesses. Today, films made of cellulose acetate are used, which are offered industrially in a wide range of different thicknesses. Foils with a thickness of 0.1 to 0.2 mm and polished on both sides are particularly suitable for producing foil prints. Thicker films are - although they bend and curl less - more difficult to handle because they are too rigid and the images lose contrast with increasing film thickness .

use

The method is particularly suitable for the documentation of lithological details of carbonate rocks or clastic rocks with a carbonate matrix . More rarely, foil prints are also made from pebbly or clastic sedimentary rocks . Rocks with little or no porosity are usually more suitable for the method than holey or porous rocks, since this way a complete wetting of the rock surface with solvent can be better guaranteed. To reduce the porosity of the rock, it is sometimes necessary to soak the rock sample under vacuum with a resin and then to grind it again.

In contrast to thin sections , film prints can also be made from significantly larger pieces of rock (up to 0.5 m × 0.5 m). Often the film prints - pressed in glass plates and as photographic negatives - are documented. The production of foil prints is more time-saving and cheaper than the production of thick or thin sections.

Individual evidence

  1. ↑ Béatrice Oesterreich: A contribution to the geochemical facies diagnosis of Devonian reef carbonates in the eastern Rhenoherzynikum (Elbingeröder complex, Harz) . Greifswald 1987, p. 13.
  2. ^ PJ Davies, R. Till: Stained dry cellulose peels of ancient and recent impregnated carbonate sediments . Journal of sedimentary petrology, Volume 38, 1968, pp. 234-237.
  3. ^ A. Katz, GM Friedman: The preparation of stained acetate peels fort he study of carbonate rocks. In: Journal of sedimentary petrology. Volume 35, 1965, pp. 248-249.
  4. ^ John Miller: Microscopical techniques: I. Slices, slides, stains and peels. In: Maurice Tucker (Ed.): Techniques in Sedimentology . Blackwell, Oxford / London / Edinburgh / Boston / Palo Alto / Melbourne 1988, ISBN 0-632-01372-9 , p. 101.

literature

  • John Miller: Microscopical techniques: I. Slices, slides, stains and peels. In: Maurice Tucker (Ed.): Techniques in Sedimentology . Blackwell, Oxford / London / Edinburgh / Boston / Palo Alto / Melbourne 1988, ISBN 0-632-01372-9 , pp. 101-104.