In the intermediate realm

The exhibition at the Museum Koenig opens up an unknown and fascinating world of mineral imagery to the curious viewer, whose incredible wealth of colours, structures and variety of motifs can only astonish, and which, beyond the scientific message, triggers the most diverse emotional sensations. In this way, pictures are created that are sometimes cheerful and dreamlike, sometimes serious and profound, expressing the diverse experiences of human existence; following Paul Klee's statement: 'Art does not reproduce the visible, but makes visible'.

THE ORIGINS OF PETROGRAPHICS

Geoscientists first examine solid sample material (minerals, rocks, ores, materials) with a polarising microscope before using highly developed analytical methods. Microscopic processing has the advantage of being powerful, cost-effective and time-saving. Its strength is also the non-destructive and relatively high-resolution characterisation of material properties (phase composition, microstructure).

The examination in the transmitted light microscope is carried out on wafer-thin, finely ground or polished sample discs (thin sections). Many materials then become translucent, so that when viewed in bright field, fine structures (grain boundaries, cleavages, cracks) and colour appearances become visible that remain hidden to the naked eye (Fig. 1). When viewing the thin section between two perpendicularly oriented polarisers, a wide variety of interference effects occur due to the often optically anisotropic behaviour of the minerals. They cause the grain structure to appear in different interference colours (Fig. 2). By inserting auxiliary optical objects (lambda plate, lambda/4 plate, quartz wedge) into the beam path of the microscope, further mineral-specific interference colour effects are created (Fig. 3).

High-resolution photomicrographs form the basis of the image composition. In this case, they are taken with the Canon EOS 70D SLR camera, which is connected to the phototube of the LEICA DMLP polarising microscope via a high-quality adapter (ASKANIA, Mikroskop Technik Rathenow). The digital post-processing and artistic alienation of the photomicrographs is carried out using the Adobe Photoshop Professional programme. The objects of photomicrography are predominantly thin sections of a wide variety of rocks, less frequently of technical materials or synthesis products. They come from the large pool of my own research material and the teaching collections of mineralogical institutes (Bonn, Clausthal, Marburg, Kiel).

MICHAEL MARTIN RAITH

*1940 in Madrid
Professor emeritus at the Institute of Geosciences at the University of Bonn since 2005

His research focussed on the internal structure and evolution of the Earth's Precambrian
crust, in particular the rock-forming processes taking place at depth. He travelled extensively to the Kola Peninsula, Lapland, Greenland, Sri Lanka, Madagascar and repeatedly to India.

The intensive microscopic processing of a wide variety of geomaterials over the course of a long professional life awakened his enthusiasm for the fascinating visual world
of a hidden microcosm at an early stage. He is less interested in reproducing purely aesthetic microphotographs than in tracking down and creating motifs that express inner moods and messages. His leitmotif is Paul Klee's statement "Art does not reproduce the visible; it makes visible."

The enormous possibilities of digital microphotography and image processing have made a decisive contribution to turning his artistic inclination into a passion.