Get an overview of Hjorths Factory here.

  • Hjorthsfabrik _vejviser

Get an over view of Hjorths Factory here.

A: Earlier wood storage now exhibition galleries and shop.

B. ground fl. Furnace Rooms.

On your left the old wood fire kilns on your right the gas and electric kilns in use today.

Furnace Rooms

The Wood fire furnaces. These kilns would take app. four days to pack closely with ceramics. The front doors were closed with stones and mortar and the wood was introduced from underneath, below floor level. When the kilns had reached top temperature the wood log holes were also closed.These furnaces are from 1910 and were in use up until 1964. The wood was collected from the factory's own Forrest south of Rønne. Gas & Electric kiln room these furnaces are in use today for biscuit firing and reduced glost firing. The use of modern kilns has made the firing circle less complicated - in the early 1900s two men would have tended the wood fire kilns for 48 hours - it was hard manual labour with few breaks. Every fourth to sixth week enough ware was ready to fire. Today workers can leave the furnace to build up heat and plan the firing to reach high temperature during normal work hours. However we still need pyrometers and seger cones to monitor the temperature inside the kiln in order to check the glaze is fully melted before we take the temperature down slowly. In historic times it took three days for the furnaces to cool down. The brown glazed ware is placed to the left hand side of the kiln close to the gas flame. If placed on the right hand side the glaze will not reach to its silky iridescent quality. For this reason one off pieces with different glazes are introduced to the kilns right hand side. The Japanese black tenmoku glaze, white tin glazes and celadon glazes can fire in a less reduced atmosphere. Seger cones. cones are pyrometric devices that are used to gauge heat work during the firing of ceramic materials. The cones, often used in sets of three, are positioned in a kiln with the wares to be fired and provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature. Thus, pyrometric cones give a temperature equivalent, they are not simple temperature-measuring devices.

B. Top. Fl. Works shop rooms.

C. Ground fl. Filter press: Filter pressing is a separation process, specially employed by solid/liquid separation using the principle of pressure drive, provided by a slurry pump.The major components of a filter press - are skeleton and filter pack. The skeleton holds the filter pack together while pressure is being developed inside the filter chamber. It however can only hold a specific volume of solids. When the clay leaves the filter press 75% of the volume i. e the water is separated from the clay mix. Clay Room. Here the clay is kneaded. The slabs from the filter press are laid on zinc plates in layers with Chamotte and slip in between. This process was done by manual workers. The clay was packed in cloth to keep the moisture in. The manual workers would make sure there was enough clay for the production at all times. They were responsible for the mining, the cleaning and crushing of the clay and later the blunging and filter pressing of the clay. It was very important that the clay was cleaned from impurities as small stones or straws would make a product shatter during firing. 

Today the clay is processes in a vacuum mixer pressed into long column's and packed in plastic, this process is done once a year. 

Clay mill: 

In the Clay Mill the clay is crushed and mixed with water. Afterwards the clay is ready for slip casting. 

The clay mill not only mixes the slip but also grinds the clay to a powder. The mill is a rotating cylinder containing little metal balls. The clay mill was invented in the 1850 s after the industrial revolution and the invention of the steam power. 



A blunger is a machine commonly used in the pottery industry for mixing clay and water. A blunger usually consists of a round or octagonal tank with a mixer. Clay is added to the water-filled blunger and then mixed into a slurry, which is also called slip. 


Clay store rooms 

The oldest clay is always used first as it is has the most plasticity . While the clay matures the molecules of the compound settles back into their natural patterns which were disturbed during the cleansing process.

C. 1. Fl. 

Slip casting Room. 

The slip casting room was established at the factory in the 1970 s.  

Slip casting is a technique for the mass production of pottery, especially for shapes not easily made on a wheel. A liquid clay body slip (usually mixed in a blunger) is poured into plaster moulds and allowed to form a layer on the inside cavity of the mould. In a solid cast mould, ceramic objects such as handles and platters are surrounded by plaster on all sides with a reservoir for slip, and are removed when the solid piece is held within. For a hollow cast mould, once the plaster has absorbed most of the liquid from the outside layer of clay the remaining slip is poured off for later use. 

This slip casting room is the former decoration room. Most of the grey/brown stone ware was decorated here and the female painters were closely seated along the walls. In between them were glass plates  holding the mixed metal oxides. The work required deep concentration as all Thora Hjorths designs were very intricate. 

The small decorating room. 

Originally part of the now slip casting room. 

The factory has a long tradition of decorating their ceramics. Originally copies of Greek vases were painted with Greek motifs , mountain scenes and scenes from the bornholmian nature. The danish painters Holger Drachmann and Kristian Zahrtmann painted for  Hjorths Fabrik. Shortly before the outbreak of the 1. WW Hjorths mass produced the grey/brown ware with intricate naturalistic patterns designed by L. Hjorths daughter Thora Hjorth. After 2. WW these designs were no longer in production. 

This small room was also used by visiting artist. Amongst others -  the Czech born sculptor  Gertrud Kudielka modelled most of figurines here. 

D: Ground fl.


After biscuit firing the ware is ready for glazing. 

In the front room glazes are mixed from original chemical compounds such as flint, kaolin and tin oxide 

Our famous silky brown glaze is literally made from the bornholmian bedrock as it encompasses local clay from Sose and Rønne granite. 

In the back glazing room wares are shellacked on the bases and decorated with a clear iron based glaze on the inside and when dried the piece is dipped into the surface glaze. The finish where the two glazes meet are hand painted with a painters brush.  For some glazes we now use airbrushing. 

The glazes becomes a glass during firing and create and extra skin around the ceramic piece. Stone ware is however fired at high temperatures and does not require glazing to be water proof. 

At Hjorths Factory the glaze firing is done in an reduced environment.  To day we use a gas fired kiln where we up until 1964 we would have used a wood fire kiln. The gas eats the oxygen molecules in the glazes and gives our brown glaze this specific silky iridescent surface. If we had glost fired the brown ware in and electric kiln the colour would come out as milk chocolate. All the glaze recipes Hjorths Factory use are specially designed for reduction firing. Some recipes dates back to 25 AD and others come all the way from Chinese Ming Dynasty in the 1300s. Most of Europe were inspired by Japanese art in the early 1900s and Hans Hjorths stone ware experiments took their inspiration from Japanese ceramics. These glazes were thick and heavy floating along the walls of the pieces. Ox blood glaze, green and brown colour specks came from cobber oxides. Mostly stone ware glazes encompasses , quartz, flint, feldspar and chamotte. Biscuit firing is achieved at 900 °C and glost firing 1180–1280 °C. 

D: 1. Fl.The Turning Room. 

The Turning Room is the heart of the factory. It stands as it was build 125 years ago. At the factory's prime all the benches accommodated a thrower. The apprentice were seated at the back of the room the masters at the front. A working week in the 1880 s were 60 hours long. 10 hours a day from Monday to Saturday. A thrower was paid between 15 and 22 danish kroner equivalent to the price of 1,5 kilo rye bread or 125 grams of butter. 

Today the clay is still hand thrown into ware. Slip cast products are also finished in the throwing room. Spouts and handles for teapots are assembled here and the biscuit fired pieces are decorated with metal oxides before the glost firing. 

Figurines are also mold made in the throwing room. They are usually made of many parts and assembled afterwards. The parts are kept humid ind the humidor. 

E. Directors office and Fourth generations private quarters.

F: The Court Yard.

Bornholms subsoil contains various types of clay. Hjorths Factory originally had their own clay pit in Sose south of Rønne. The clay was brought into the court yard of the factory where sun and frost helped the clay to  mature, later it was cleansed from small stones and bits of wood. The crushed clay was mixed with water, powdered quartz and feldspar's in the large wooden barrel. To remove impurities from the clay the mixture was sifted through a series of filters and poured into large vessels on the floor. From here the clay mixture was pumped into the filter press

Clay as a chemical structure.

Clay is a fine-grained soil that combines one or more clay minerals with traces of metal oxides and organic matter.Geologic clay deposits are mostly composed of silicate minerals containing variable amounts of water trapped in the mineral structure.Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lakes and marine basins. Primary clays, also known as kaolins, are located at the site of formation. Secondary clay deposits have been moved by erosion and water from their primary location. This movement took place during the last ice age. The clay on Bornholm comes from Norway and Sweden and Bornholm is the only place in Denmark where primary clays such as Kaolin and Stone ware clay can be found. There are three or four main groups of clays: kaolinite, montmorillonite-smectite, illite, and chlorite. Chlorites are not always considered a clay, sometimes being classified as a separate group within the silicates. There are approximately 30 different types of "pure" clays in these categories, but most "natural" clays are mixtures of these different types, along with other weathered minerals. Varve (or varved clay) is clay with visible annual layers, formed by seasonal differences in erosion and organic content. This type of deposit is common in former glacial lakes. When glacial lakes are formed there is very little movement of the water that makes the lake, and these eroded soils settle on the lake bed. This allows such an even distribution on the different layers of clay. 

Clays exhibit plasticity when mixed with water in certain proportions. When dry, clay becomes firm and when fired in a kiln, permanent physical and chemical changes occur. These reactions, among other changes, cause the clay to be converted into a ceramic material. Because of these properties, clay is used for making pottery items, both utilitarian and decorative, and construction products,such as bricks, wall and floor tiles. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware, and porcelain. Prehistoric humans discovered the useful properties of clay. Some of the earliest pottery shards recovered are from central Honshu, Japan. They are associated with the Jomon culture and the deposits from which they were recovered have been radiocarbon dated to around 14000 BC. Depending on the content of the soil, clay can appear in various colors, from a dull gray to a deep orange-red.

Clay tablets were used as the first known writing medium, inscribed with cuneiform script through the use of a blunt reed called a stylus. Purpose-made clay balls were also used as sling ammunition.Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, dishware, and even musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is also used in many industrial processes, such as paper making, cement production, and chemical filtering. Clay is also often used in the manufacture of pipes for smoking tobacco. Until the late 20th century bentonite clay was widely used as a mold binder in the manufacture of sand castings.Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage.Recent studies have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.

Clay as a building material. Clay is one of the oldest building materials on Earth, among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of the world's population, in traditional societies as well as developed countries, still live or work in a building made with clay as an essential part of its load-bearing structure. Also a primary ingredient in many natural building techniques, clay is used to create adobe, cob, cordwood, and rammed earth structures and building elements such as wattle and daub, clay plaster, clay render case, clay floors and clay paints and ceramic building material. Clay was used as a mortar in brick chimneys and stone walls where protected from water.

Medical and agricultural uses.A traditional use of clay as medicine goes back to prehistoric times. An example is Armenian bole, which is used to soothe an upset stomach, similar to the way parrots (and later, humans) in South America originally used it. Kaolin clay and attapulgite have been used as anti-diarrheal medicines.

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