Belgian chunk
The Belgian Brocken is a natural stone quarried near Vielsalm in the Belgian Ardennes , which is used as a whetstone or whetstone for fine grinding.
history
The history of mining in the pits of the Belgian Ardennes (mountains) can be traced back to Pliny the Elder (Roman writer). Even today, this deposit is unique worldwide because of its composition: In the approx. 480 million year old, rather soft, gray-yellow sedimentary rock made of volcanic ashes and clays, high proportions of the finest garnets (5–20 microns ) are embedded. After diamond , corundum and beryl follows garnet of hardness by a wide margin. Similar to a soccer ball, the surface is divided into facets ( rhombic dodecahedron ). Precisely these characteristics, namely the hardness and roundness of the grains, lead to the excellent sharpness properties.
De Blauwe Wetsteen
In cooperation with laboratories at the University of Liège , a new line of the last remaining mine had the geologically close layers of the traditional yellow Belgian chunk (Coticule) examined in 1996/97. A high-quality sharpening stone with similar properties was discovered, only with a blue-gray color, which comes from iron oxide . It contains approx. 30% stored grenade, which makes it a little slower than the well-known yellow chunk, but more durable. The great advantage of the blue stone is that the layers that occur can be used in thicknesses of 15–20 cm, which means that beautiful, large bench stones can be cut again . In addition, this blue stone is also suitable for profile shapes and - in contrast to other much harder profile stones - its shape can be adapted to individual needs on simple sandpaper.
Coticule
The traditional (yellow) stone contains 35–40% garnets. The thinnest layers deliver the best quality, which is why they are cemented with a layer of slate for stabilization. For this reason, the stone can seldom be offered as a bench stone, the polygonal shape, referred to as “chunks”, which gave the stone its name, is more common.
Mode of action
When peeling off of tool steels , the resulting during grinding burr is removed and the cutting polished. If the blade of the tool rubs over the evenly fine-grained surface of the Belgian chunk that is moistened with water, the grenade emerges, detaches from the bedrock (grain breakout) and thus forms a thin paste with the water and the rubbed-off matrix of ash, clay and mica who have favourited abrasive paste. The curves of the grenade penetrate the steel only slightly and remove fine chips from the metal. The hardness of the garnet, however, causes very sharp abrasion. Due to the almost round shape of the crystals, however, there are no scratches, but a fine polish. This combination of speed and delicacy is unique in the world. Through them, a sharpness can be achieved with which z. B. the wood fiber can be cut cleanly across with cutting tools.