Porcelain products have long been valued no less than gold and were available only to the noble and wealthy people. The secrets of making porcelain dishes were carefully kept under seven seals and seven locks. These facts show that porcelain products are an attribute of luxury and have great value. This article describes the most famous types of porcelain, their differences, advantages, and features of care for each of them. You will also learn about the production process and details of decorating porcelain products.
Such a relevant material for the production of tableware, figurines and other products as porcelain is often used and has several types, among which there are three most famous: hard-paste, soft-paste and bone china, which is a compromise between soft-paste and hard-paste porcelain. Before going to the specifics of each type, it is worth noting that soft-paste porcelain is used primarily for the manufacture of esthetic products, while hard-paste porcelain is usually used in engineering and in everyday use (tableware).
Hard-paste porcelain is also called true porcelain. This material has always been considered as a standard of excellence for masters. This type was made from petuntse, or china stone (a feldspathic rock), ground to powder and mixed with kaolin (white china clay), while the ratio of ingredients could be completely different. For many years, Europeans have tried to unravel the secret of true Chinese porcelain. This was done about 1707 at the Meissen factory in Saxony by Johann Friedrich Böttger and Ehrenfried Walter von Tschirnhaus.
The composition of this type is characterized by a higher content of kaolin or white clay and a lower content of quartz and feldspar. The characteristics of hard-paste porcelain depend on the proportion of two main substances (kaolin and feldspar): the more its mass contains kaolin, the more difficult it is to melt and the harder this mass becomes. This mixture is ground, kneaded and then dried to a degree when it is capable to take the form of a dough-like state.
There is a plastic mass that can either be cast (material is poured into a mold) or throwed on a Potter’s wheel. Products made of hard-paste porcelain are fired twice: first time – without glaze at 600 – 800 °C, and then with glaze at a very high firing temperature of 1400-1460 °C. Sometimes additional dolomite or calcareous spar is introduced to enhance transparency. Hard porcelain is covered with hard glaze. Thin varieties are covered with a glaze of spar without limestone, so the products have matte, milky cream color. But the simpler varieties are covered with a completely transparent limestone glaze. Glaze and porcelain mass consist of the same substances, only in different proportions.
Thanks to this, they are connected, and the glaze can no longer be beaten off or detached. As a result of all this, true porcelain is characterized by high heat resistance, strength, and clear bell ringing. The color version of hard-paste porcelain dilutes the grayish or blue hue, and there are tiny pits on the surface, due to which this material is often compared to eggshells. Thanks to the complex production technology and multiple firing, this type of china has an impeccable strength and true porcelain tableware is not only solid, but also very beautiful, as you can see by looking at products from manufacturers of Gzhel and the Imperial porcelain factory. Our store also offers you wonderful chess sets made of hard-paste porcelain that can be a valuable gift for both a connoisseur of rare and beautiful things, and a chess player.
The first European soft-paste porcelain was made in Florence about 1575 at workshops under the patronage of Francesco I de’ Medici. Soft porcelain, also called artificial or fine, consists mainly of mixtures of vitreous substances – Frit, containing sand or flint, saltpeter, sea salt, soda, alum, and crushed alabaster. After a certain time of melting, a marl containing gypsum and clay is added to this mass. We are talking about a fused vitreous substance with an addition of clay. All this mass is ground and filtered, brought to a plastic state. The molded object is fired at 1100-1500 °C. The glaze is mainly made of glass, that is, of a fusible substance rich in lead oxide and containing sand, soda, potash, and limestone. Glazed products are subjected to secondary firing at 1050-1100 °C, when the glaze is combined with the shard.
Soft-paste porcelain does not differ from hard-paste porcelain in solidity but firing soft-paste porcelain forms more liquid phase than firing hard-paste one, and therefore there is a higher risk of deformation of the workpiece during firing. Artificial porcelain is more diverse in chemical composition and has a higher content of quartz and feldspar. Thanks to all this, soft-paste type of porcelain has a more delicate white color, sometimes characterized by an almost creamy tone, and it is also more transparent than hard. But the heat resistance of soft porcelain is much lower than that of true. Soft porcelain products are a real fantasy game that can become a part of your feast.
As for bone china, it represents a well-known compromise between hard-paste and soft-paste porcelain. Its composition was discovered in England, when Josiah Spode the Second added calcined bones to the hard-paste porcelain formula, and around 1750 its production began. This type of porcelain consists of admixtures of quartz, kaolin, and bone ash, from which porcelain got its name. Bone ash makes possible easier melting. Bone porcelain is fired at 1100-1500 °C. Its glaze is basically the same as on soft-paste porcelain, but contains, in addition to lead oxide, a certain amount of borax for better connection with the cover. At the appropriate caloric heat, this glaze melts and is firmly connected to the shard.
Bone china is harder than artificial but is inferior in this characteristic to true porcelain. Bone porcelain is extremely durable, famous for its exceptional whiteness and delicate transparency. The durability of products made of this material is due to the melting of the main components during the firing process. Thin walls of bone china products allow you to view your own fingers in the light through the walls. The voids that appear between the particles of white clay are filled with bone ash, which eliminates the eggshell effect that is present on the surface of hard-paste porcelain dishes. That is why, products made of bone china have a higher cost compared to dishes made of hard-paste porcelain.
As you have noticed, all types of porcelain differ from each other in characteristics but, despite this, they all have common features of care. Hot water, as well as any active and abrasive detergents can spoil the surface of porcelain. Therefore, it should be washed in warm water with the use of soft detergents. So, all types of porcelain differ from each other and have their own features and advantages. We sincerely hope that you will find the type of porcelain tableware that you will especially like in our online store.
Throughout its existence, porcelain has constantly changed: not only the types of products made from it and their forms, but also the methods of decoration. There are three main techniques of porcelain tableware decoration: underglaze and overglaze painting, as well as relief decor. Each of these techniques is of considerable interest.
Underglaze painting of porcelain dishes is not used very frequently today due to the limited range of paints. This technique is typical for antique Chinese porcelain. The technique of underglaze painting involves applying paint to a finished but unglazed product. Firing at a temperature of 1350°C is performed only after the drawing is completed. Paint is applied with a pen or brush, also sprayers and special underglaze pencils are often used for modern porcelain. It is very important that the consistency of the dye is sufficiently dense so that it does not spread over the surface of the porcelain.
The quality of the result depends on the characteristics of the selected colors. So, one of the main requirements is heat resistance. During the firing process, the paint should not fuse with the glaze or dissolve in it. Chemical stability is equally important. To provide it, kaolin or aluminum oxide is added to the dyes. The paint must be fused with the porcelain itself in the process of firing.
The following colorants are mostly used for underglaze painting of porcelain sets:
- Containing iron, manganese, zinc, and chromium oxides. Adding these oxides gives a black or brown color to the drawing.
- Dyes containing alumina, cobalt salts, and zinc oxide. The finished drawing made with this dye will have a blue color. Dutch blue-and-white tiles and Chinese porcelain inspired Russian masters to create a two-color drawing with only cobalt. With the help of cobalt, the Imperial porcelain factory created its world-famous cobalt net, and Gzhel – its traditional patterns.
- Spinel-based dyes. Spinel is a mineral containing aluminum and magnesium oxides. Dyes can have different colors. The use of spinel provides paints with thermal stability, shape, and color stability. Such dyes do not melt into the glaze during firing and do not mix with it.
The technique of underglaze painting has some features. So, underglaze paints become brighter after firing, their color may change. Therefore, a trial application of dye and firing is often performed before painting the product. This is necessary to evaluate the reaction of the paint to firing under the glaze with a specific composition. The finished underglaze painting has soft, smooth lines, so it is used to depict complex, “textured” elements — foliage, plumage, fur, etc.
Overglaze painting is considered to be simpler in comparison with underglaze. Paint is applied to the glazed product and then the porcelain dishes are re-fired in a muffle furnace. This allows to pin the image.
Today, there are two main methods of overglaze painting.
- For standard overglaze painting (low-fired glaze), the dye is applied to the already fixed enamel, after which it is fired at a temperature of 700-900°C. The relatively low firing temperature reduces the requirements for the characteristics of paints. On the other hand, the painting itself becomes less durable. It can have a tangible tactile relief since the colors are melted into the glaze, without dissolving in it.
- For overglaze painting with high-fired glaze, paint is also applied to the fixed glaze. After that, the product is fired at a temperature of 1200-1350°C. As a result of firing, the paint “melts” into the glaze. At the same time, the drawing does not blur, it remains clear. This technique allows to create image that is resistant to mechanical influences.
For overglaze painting, paints of various colors are used. Their composition is also diverse. The main requirement is thermal and chemical resistance, as well as a normal reaction to interaction with the glaze. Dyes with the addition of precious metals (silver, gold, platinum) are often used for overglaze painting. When preparing the paint for work, turpentine oil must be used. With its help, the paint is brought to the desired consistency. Overglaze painting of porcelain sets makes it possible to create different drawings with both smooth and soft lines, and sharp strokes.
It should be pointed out, of those paints that are used for painting porcelain products, a special position is assigned to the group of paints based on metals of noble origin. Among them, the most common are paints with gold. Gold overglaze paints are often used for low-temperature firing of porcelain products. Decorating porcelain with platinum or palladium creates “silver” plating (liquid silver is rarely used). Decoration of porcelain items with precious metal paints takes place after painting the color palette and fixing it in the oven in the final stage, since such paints are fired at an even lower temperature of about 700 °C. After firing gold or platinum paint preparations of precious metals form a metal oxide film on the surface of the product.
Although the relief decoration is not a painting, it is of considerable interest. This is a classic technique for decorating porcelain dishes that was used in Europe. Relief decor involves the production of individual small elements for decorating porcelain. This can be flower petals, leaves, curls, fragments of patterns. These elements are fixed directly on the porcelain, for which the engraving method or perforation are used. Glue compositions are also used for fixing. Relief elements are made of porcelain and painted in classic techniques. They make the appearance of porcelain more original and expressive. However, dishes with a raised decor are considered more fragile — they require special care and right storage.
Paints are also divided into the types. Firing of paints, which is necessary to preserve the pattern on the surface of a porcelain product, occurs under different temperature regimes and conditions. So, the paints have a different composition.
Porcelain paints consist of coloring components (pigments), glass-forming components (fluxes), and tint components. The main difficulty in making ceramic paints is to obtain pigments that do not dissolve much in the glaze melt and do not lose their color at a high firing temperature.
A pigment is a dye in the form of a powder obtained by the oxidation of various types of metals. However, pure pigments are not used for coloring porcelain products, because they do not withstand firing at high temperatures. Therefore, fluxes are added to the pigments – colorless fusible oxides (for example, oxides of silicon, potassium, sodium, boron) also in the powder state. The flux acts as a binding agent that melts in the furnace during firing, combines with the glaze and gives the paint a gloss. Mixing fluxes with pigments is the way to get colored melts when heated, almost analogous to colored transparent glass or opaque smalt. Calcined quartz, burnt kaolin, porcelain parts, and some oxides (silica, alumina) are used as tint components.
The brightness of the colors on dishes and figurines of previous years is since lead and some other heavy metals were added to the paint. Now the content of harmful metals in paints is clearly regulated by acceptable standards. Our companies do not use heavy metals to create their own palette of paints for porcelain.
How are paints for painting created? The pigment with fluxes is rubbed until it turns into a homogeneous mass without lumps. Powder paint is mixed with water-based mineral oil to a sufficiently thick consistency, and only then the paints can be mixed to obtain different shades. There are several features, some paints can be burned several times, some not. Or, for example, cadmium and cadmium-free paints are fired at different temperatures, so depending on the type of paint in the painting, strokes of different thicknesses are used or a different number of layers of coloring matter are applied, or the corresponding order of paint application in the drawing can be determined.
Porcelain painting is an ancient and complex art. The surfaces of porcelain products are smooth and slippery, while excess paint is not absorbed by the surface, as it happens when painting on paper or canvas. It is very difficult for the artist to maintain the required thickness of the paint layer. If a thick layer is obtained, the paint will boil during firing, and the product will be spoiled. But too thin layer is dangerous for the result. During firing, the paint can give a very pale shade or even burn out, become matte. Paints change their color during firing, so the artist must already in the process of painting porcelain objects imagine how the colors will look after firing. To obtain shades, artist may use the method of mixing paints. However, not all colors can be mixed. This depends on the chemical composition of the paint. For example, paints containing cadmium should not be mixed with cadmium-free paints, since they are fired at different temperatures. All types of porcelain painting depend also on the quality of the brushes. When painting porcelain products, brushes of different thicknesses are used. Sometimes the brush pen consists of just a few hairs. Brushes of the highest quality are made of hand-knitted squirrel wool. Artists also use such tools as pen, sponge, and others. Creation of a fantastic porcelain product is the experience of generations of masters and artists, it is a manual casting and painting of every detail, it is the highest quality materials and an individual approach to each work. Porcelain hand-painting contains a whole history, it reflects all the trends in the development of art, it reflects the realities and interests of humanity of a particular era, so fans of art estimate its significance and its features when choosing items for their collections.