Sharpening History. Swedish Gotland Stone

Since the early Middle Ages, the island of Gotland, the largest of the Swedish islands, has been famous for its sharpening stones. The rich deposits of local sandstone provided the Vikings not only with building material, but also with an excellent abrasive known throughout Europe.

Gothland is Sweden's largest island. It is one of the main strategic military beachheads of the past in the Baltic Sea. It is located about 100 km from the Swedish mainland. The island is a plateau, composed of Silurian limestones and sandstones, the prevailing elevations are 30-50 meters, and the highest point is a hill Loista-head (83 meters). The geological structure of Gotland is based on rock of the Silurian Period, which is the third Paleozoic period following the Ordovician and the Devonian. It is believed to have started at 443.8 ± 1.5 million years ago and ended at 419.2 ± 3.2 million years ago, a total time span of about 25 million years. This is the shortest period of the Paleozoic. The rock deposits that arose then are called the Silurian system. Sixty percent of marine life died out during this period, and fossils made up the bulk of the rock. During the Silurian period, part of the continental plate area was occupied by shallow marine basins dominated by shallow shelf carbonate sediments and lagoonal deposits.

In fact, the island of Gotland consists of a sequence of Silurian-age sedimentary rocks extending from north to southeast. The main strata of limestones and shales consist of thirteen blocks with a stratigraphic thickness of 200-500 meters. The sedimentary rocks formed on Gotland were deposited in a shallow, hot and salty sea at the edge of the equatorial continent. The water was never more than 175-200 meters deep and became shallow over time. The growth of the rocks began when the sea was 50-100 meters deep. The calcareous rocks have weathered over millions of years into characteristic karstic rock formations, formed mainly by corals and brachiopods (a distinct species of marine solitary bottom animals), which are distributed all over the island. Gotland has a mostly depressed topography consisting of flat surfaces on which the last glaciation has left thin covers of fine-grained boulder-like calcareous clay. 

The composition of the Gotland sandstone, characterized by high homogeneity and fine grain size of the deposits. It has a gray color with some shades, depending on the site and the layer from which it is extracted. At the same time, the stones under the influence of outside air become brown over time. The matrix that forms the cement between the grains of the stone usually consists of 5-25% calcite. The high proportion of CaO (calcium oxide) and CO2 (carbon dioxide) is also accompanied by substantial amounts of aluminum, iron, magnesium and potassium oxides. The stone usually contains a small portion of amorphous silica. Sandstone grains consist mainly of quartz and feldspar, with small phenocrysts of mica and calcite. The sandstone also contains insignificant amounts of pyrite and very small amounts of glauconite, limonite, and jarosite. The grain size of the Gotland stone varies from 0.1 to 0.2 mm. It is very porous and has a hardness of about 6 to 7 on the Mohs scale.

The main stone deposits are found in the Silurian Burgsvik lowland, not far from the coast in the south of Gotland. The formation is about 35 km long on the west bank of the Storsudret. The sandstone is located between layers of limestone and is not more than 6 m thick, the formation is not homogeneous, but mixed with limestone and layers of clay. The structure and orientation of the stone indicate that it was formed as sandbanks in the shallow waters near the coast.

Gotland stone has been known throughout the Baltics since the early Middle Ages. It was used for building and decorating buildings. Over time it became very popular and became one of the most common decorative stones in Sweden. This is due to its homogeneity, softness and good workability. Associated with the use of sandstone is the great cultural tradition of marking pictographs on stones and creating sculptural images of the Vikings. Today scholars refer to it as "memorial stones" or "picture stones". Gotland is considered the center of this tradition, and modern archaeologists have studied pictographs left on stones made of both sandstone and local soft limestone. It is assumed that the manner of writing some symbols spread in the twelfth and thirteenth centuries from Gotland throughout the Baltic region.

From the 13th century until the middle of the 14th century, sandstone was actively used as a building material for friezes and porticoes in Catholic churches. Some of the most famous churches that were built entirely of Gotland stone are in Och, Sundre, Hamra and other settlements on the island. The use of sandstone declined somewhat under Danish rule from the 14th century.  However, under the influence of the Dutch Renaissance, ornamental stone became in demand again as early as the 16th and 17th centuries, which led to the opening of new quarries. They were under the direct supervision of the whole dynasty of Danish kings Christian III, Frederick II and Kristan IV. Experienced stonemasons were specially sent from Denmark to Gotland to resume stone production, where there was a shortage of skilled workers. During this period Kronoborg Castle in Copenhagen and several other castles of influential Danes were built. It also became fashionable to use Gotland stone for facades, sculptures and porticoes in the palaces of Stockholm, as well as in Germany and Poland.

Mining of the rock continued into the 17th century, when Gotland became Swedish. In the industrial era, the demand for sandstone came from local pulp mills, sugar mills and steel mills. However, the use of Gotland stone as a building material gradually declined from the early 20th century and declined sharply after 1920. Even today, though, stone is still mined in limited quantities, primarily for restoration purposes.

The use of sandstone for sharpening has been known since antiquity. Already in the Stone Age, and later in the Viking Age, it was used to make sharpening blocks, which are found at burial sites. Sandstone bars had both a coarse structure with high abrasiveness and were polished to a finer surface for grinding. It was used with both water and oil.  The abrasiveness of sandstone is traditionally estimated at 2000-5000 grit by the JIS system, depending on the amount of impurities. Like the famous Beindheim sandstone in the past, the Holland stone is considered quite fast, but is more suitable for pre-finish sharpening and requires a finer stone after itself for finishing the blade. The main disadvantage of any sandstone is its brittleness and tendency to chip.

In the 19th century there were private craftsmen who supplied sharpening bars to the market, but there was no centralized sale of stone and there is little written evidence of its properties of that period. In one of the cities on the island, Brugsvik, there is now a stone museum with ancient tools and machinery for mining stone, and a memorial to the families of the workers who quarried stone for many decades. A local company, Gotlandsbrynet, has been producing and selling hand-sharpening stones for knives and tools made from Gotland sandstone since 1982. They are sold both in the museum itself and in stores in neighboring towns. Gotland stone continues its history.