Ceramic pottery glazes are thin, glassy coatings applied to the surface of clay products. This layer is formed by the firing process.
Ceramic pottery glazes are the basic raw material for making Ceramic pottery glazes. It is a powder mixture of silicates or borosilicates in the form of glass flakes. It is obtained by melting the mass and its rapid cooling. The thermal impact breaks the glass into fragments. The fragments are then ground into powder.
Ceramic pottery glazes can be divided into two main categories, which include raw and molten frit (sintered) types of Ceramic pottery glazes.
Refractory materials – temperature range 1200-1420 degrees.
Fusible – temperature system of about 800-1200 degrees.
Ceramic pottery glazes of the first group are used in firing procedures of porcelain or semi-porcelain, stoneware, and faience pottery. Ceramic pottery glazes of the second group are used for underglazes of low-temperature clay masses (grizzly red clay, MKF2, etc.).
If the formulation of Ceramic pottery glazes is considered in detail, it may look like this.
Alkaline monovalent and divalent metal oxides.
Lead oxide and iron oxide (as fins).
Some silica and other oxide additives (acidic).
Al, O2, Gr2, O3, Fe2, O3 oxides.
Ceramic pottery glazes can be either transparent or opaque (opaque). Opaque glazes or enamels are obtained by mixing transparent glazes with insoluble or semi-soluble compounds, or by forming fine, crystalline or gaseous phases in the Ceramic pottery glazes themselves (at a defined temperature). Glazes can also be glossy or matte, colorless or colored.
The glazing process consists of dipping the colored object into Ceramic pottery glazes in a container or sprinkling the product with Ceramic pottery glazes. Ceramic pottery glazes can also be sprayed on the surface of the object or applied with a brush.
Some specific characteristics of the effect of oxides on the properties of Ceramic pottery glazes
Under the influence of silica, the refractoriness and viscosity of Ceramic pottery glazes increase and a decrease in the coefficient of thermal expansion can be observed. Silica can be introduced in the form of quartz particles, clay inclusions, or kaolinite. If the quartz is ground too finely, fine, thinning cracks may appear on the surface of the coating. This is commonly referred to as “Zephyr”.
If titanium oxide is added to the glaze, it increases the chemical stability and also helps the crystallization process, and the glaze may become subdued.
When zirconia is added to Ceramic pottery glazes, both chemical stability and fusibility are improved. Zirconia can also be introduced under the name zirconium (zirconium silicate).
If the tin oxide is added to Ceramic pottery glazes, strong passivation of Ceramic pottery glazes can be observed. However, at the same time, an increase in the humidity resistance of the glazes can also be noticed.
If cerium oxide is added, it will smother the glaze very much.
Boric anhydride as a fin has the property of making the product appearance bright and increasing hardness, and also significantly reduces the sensitivity of cake appearance. It is often added as boric acid or boron.
In addition, alumina improves the refractoriness index and also reduces the probability of scaling.
Iron oxide is a coloring oxide and is a strong melting agent. the use of this additive is generally discouraged in Ceramic pottery glazes.
Among coloring oxides, chromium oxide is a beneficial addition to Ceramic pottery glazes – increased chemical resistance, hidden appearance, and smooth product surface.
The strongest melting agent is lead oxide, which induces longer melting intervals during the firing process. In addition, this segment makes the product glossy and improves the filling of the glaze. But you have to be especially careful with this element – it is quite toxic. It should be introduced into the charge, which is a special solution of the original composition in the form of strikes.
The melting properties of copper oxide are similar to those of some additives, but its effect on gloss and pouring is rather small. This additive can give the glaze a blue as well as a red hue.
A special fusible substance in glazes is calcium oxide, which creates a matte surface. A weak fusible occurs in overglazes and a thick fusible in underglazes. It has the property of reducing the susceptibility to zephyr and also promotes crystallization. However, calcium oxide may reduce the melting temperature of the glaze during firing. It can be introduced into the charge as marble or Opoka, as well as chalk inclusion.
A stronger fusible agent than calcium oxide is magnesium oxide, which makes the glaze harder and firmer, as well as being elastic when filled.
Zinc oxide is not bad either, it is a good smoothing agent, dulls the glaze, adds magnesium oxide, and increases the temperature growth coefficient (C.T.R.).
The addition of sodium oxide to Ceramic pottery glazes also increases the temperature growth coefficient. It is also no less strong fusible and may increase the tendency to ze, but also reduces the hardness properties and may weaken the resistance to chemical attack. It is more convenient to introduce this additive into the charge in the form of borax or soda.
Reduced fire glazes, commonly known as Ceramic pottery glazes, can produce a beautiful metallic luster during firing to the level of the metal oxides contained in such Ceramic pottery glazes. The greatest possibility of obtaining this effect is the use of Ceramic pottery glazes containing silver compounds and copper inclusions. these components are almost reducible to the natural tones of the above-mentioned metals.
Absolutely all additives can be sintered or sintered, the only exception being kaolin, which is introduced into Ceramic pottery glazes during the process of grinding the abrasive.
The material, freed from carbon dioxide gas and water at certain heating temperatures, forms the necessary oxides and is an additive for boric acid, borax, lead agents as well as soda ash, potash, chalk, and feldspar.
Cooking Ceramic pottery glazes
If you need to make transparent glazes, you can do it even on your pottery at home. You need to crush the glass and immerse it in the prepared water while it is still hot. The glass pieces should become cloudy and covered with small cracks. In this case, you have received dynamite, from which the mass of the later business to make the glaze.
The next step is to grind the glass mass into a white powder. It is easy to do this with a mortar or ball mill. The resulting flour should be sifted through a sieve with very fine holes (for convenience, you can use a stocking of Capron). After mixing the glass powder with some glue or silicate glue, you should end up with a thick, white liquid – this is Ceramic pottery glazes.
If you need to get a white, dull glaze, you should add 5% or 6% zinc oxide, barium sulfate, or tin oxide to the prepared mass. On the contrary, if you want to make a transparent glaze, you can add some oxides of different metals so that you can get glazes of different colors.
Due to insufficient firing, a mat glaze is obtained. In general, the top of the glaze should be covered with small protrusions and depressions.
Unfortunately or fortunately, few people nowadays prepare Ceramic pottery glazes by hand – various shades of Ceramic pottery glazes can be bought in specialized stores.
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