Ceramics
The process starts with a template – a prototype, sketch or model – which is processed in the workshop to produce plaster moulds, which liquid clay is poured into. The manufacture is based on using high-quality powdered white clay from Germany, which is made into a pouring mixture according to a tested recipe.
The plaster moulds are made so as to draw the water from the clay, producing rigid walls of the clay products along the inner walls of the mould. Once the product dries up and hardens, it is removed from the mould. What follows is a lot of handiwork: retouching, assembling, bonding, adding, taking – all depending on the specific product. Each product has its own specificities, is marked by its own problems and poses its own challenges.
Afterwards, all products undergo air drying. When it comes to clay, proper drying is highly important to avoid cracking, deformations and similar. Once the products are dry enough, another round of retouching is in order (cleaning and brushing) before baking the clay for the first time. The first baking is referred to as "biscuit burning”. It requires a temperature ranging from 950 °C to 1000 °C and takes 9 hours on average.
After biscuit burning, the products slowly cool in the oven for a minimum of 12 hours, which is followed by glazing. Put simply, the glaze is a thin layer of glass that covers the surface of the clay. It grants the product its final appearance, rigidity and usability. Glazing is the most difficult part of the process. It depends on numerous factors, which cannot always be fully controlled. This is especially the case with effect glazing, which is a unique artistic approach. Glazing can be done with different types of application, ranging from spraying and dipping to applying the glaze with a brush.
After the glazing process, products are once again put in the oven and baked at a temperature ranging from 1050 °C to 1100 °C for approximately 6 hours. If necessary, a gold gilding process follows, which uses a special liquid that contains up to 20% of gold. Using a brush, we apply the liquid to individual parts of the product. Such a product is then once again put in the oven and baked at a slightly lower temperature ranging from 700 °C to 800 °C.
Foto: Andrej Brezec
How is made the LEAF OF PEACE
How is made the LOTUS FLOWER
Porcelain
Porcelain doesn't exist in nature, which makes it all the more special. Its charm lies in its composition, which is a combination of different materials, most of which are kaolin. Water and a homogeniser are added to the mixture. The very next day, the mixture is ready for casting. In the production of Oskar Kogoj products, only liquid porcelain is used, which is poured into plaster moulds. After some time, the porcelain is cast and what remains on the inner walls of the mould forms a cast.
Once the cast is mostly dried, it is taken out of the mould. What follows is retouching with a sponge, brush and knife, and adding, for instance a handle if we are making a cup. The product is then completely dried before the first baking takes place at 930 °C. The first baking is called biscuit baking. Biscuit porcelain is very crumbly and absorbs water due to being highly hygroscopic. After biscuit baking comes glazing. This means that a biscuit product is immersed in the liquid glaze for a few seconds. Put simply, the term glaze refers to glass with added solvents and water, which is ground into molecules. When the glaze on the product dries, the second baking process follows at 1230 °C.
With sculptures, the process of baking is slightly different. The first baking takes place at lower temperatures. The glaze gains a crackle effect, with the process taking place at even lower temperatures. Crackle glazing is characterised by tiny cracks. It is a method of effect glazing, which gives Oskar Kogoj products their characteristic appearance. Such products must be kept away from liquids and should only be cleaned with a dry rag.
If the product is to be partially or fully gold-gilded, what follows is the application of liquid gold to the glazed product with a brush or spray. Liquid gold contains up to 90 % of acids and solvents that are burned during the third baking process. Thus, only the 10 % of 18-carat gold remains on the product. The third baking takes place at 780 °C
How are made porcelain products
Glass
Most of Oscar Kogoj's glass products are produced in Steklarna Rogaška, where they have been cultivating the masterful tradition of handmade crystal glass since 1665. All the products are still handmade, and the glassmakers are assisted by the latest technology.
Fire, smoke, heat and steam vapours are certainly those elements that best characterize glassware forming. But there’s also decorative cutting, gilding, engraving … and so much more!
Master glassblowers form the molten crystal glass on pipes and then blow it into the final form using handmade wooden moulds. At least 12 pairs of hands touch each product before the final design for sale is completed.
How are made glass products
Metal
The pin badges are made of ZAMAK metal, which is a zinc alloy cast on a die-casting machine. An iron tack is attached to the back of the pin badge. The pins are galvanised with 18-carat gold, and the fastening clip is made of passivated brass. All ingredients are non-allergenic.