Cote stones are used as abrasives for sharpening or grinding metal utensils, especially knives. They are one of the most typical products of the Bergamo territory, whose virtues have been known for thousands of years and were already reported by Latin sources.
Concerning the rock deposit, the material used for the production of these whetstones is concentrated along thin layers – at most a few tens of centimetres – included in Jurassic period formations (i.e. originated approximately 200 million years ago). They surface at various locations in Bergamo, but especially in the lower Seriana Valley at Pradalunga.
The uniqueness of the material is due not only to its mineralogical composition consisting of silica granules and a calcareous cement, but also and especially to its microstructure, characterized by a texture of fusiform siliceous granules linked by a calcareous cement. These features result from the consolidation of sludge and slurry made up of tiny fragments (called spicules) of siliceous organisms such as the silicosponges.
The maximum size of the spicules is about 200 microns, i.e. 1/5 of a millimetre. Its excellent abrasive effectiveness is due to the arrangement of the siliceous spicules, which exert an action in all directions. Cote whetstones were, and still are much sought-after tools to increase the efficiency of agricultural tasks associated with crop harvesting and grass cutting. Whetting with Cote stones is particularly effective because they are very delicate and smooth, non-invasive or aggressive to the metal, and ensure great durability of the blade.
The importance of Cote stones as a valuable local resource was especially important in the past, when agriculture was the main occupation in the province of Bergamo. A proof of the material’s uniqueness and its rooted tradition is the widespread use of Pradalunga Cote stones, a cultural habit so inseparable from daily life that, kept in special stone holders (called "cuder"), they often followed the emigrants who left our valleys for the Americas or Australia. Currently, agricultural production at industrial scale is highly mechanized and does not make use of traditional tools, but in farming the use of a whetstone is still recommended to better preserve and maintain the efficiency of scythes, sickles, and other blades.