The ingredients of glaze are ever-changing, and the colors of glaze are dazzling and colorful. Some glaze colors need to be fired in a reducing atmosphere, while some glaze colors can be fired in an oxidative atmosphere. Common glaze colors that must be fired by reduction include celadon glaze, copper red glaze, and jun glaze. If the basic glaze contains chromium oxide and tin oxide as coloring agents, it will become dark green when reduced and fired and pink when fired by oxidation, commonly known as chromium-tin red. Celadon glaze uses iron oxide as a coloring agent. After reduction and high-temperature firing, the glaze color appears emerald green or light green or light aqua blue-green, which is called celadon glaze. The green glaze of celadon glaze before firing is pink because red iron oxide is used as the coloring agent; if black iron oxide is used as the coloring agent, the color of the glaze before firing is black or gray-black. That is to say, the celadon glaze is pink or black gray after glazing but before firing, but it will turn emerald green after reduction and firing. The firing method determines the color, but it is not absolutely relative. The glaze that appears light green or green before being fired is usually a glaze containing copper carbonate or chromium oxide. These glazes contain copper carbonate or chromium oxide, and It cannot be called celadon glaze because the glaze appears green. These glazes containing copper carbonate will appear aqua blue or emerald green when oxidized and fired, which is copper blue or verdigris glaze. Glazes containing copper carbonate turn into a red color during reduction firing, which is the same firing phenomenon as copper red and jun glazes. Glazes containing chromium oxide will also appear green, gray, and pink during oxidation firing due to differences in the types of alkaline raw materials. The pink color is for glazes containing chromium oxide and tin oxide, but instead When it is reduced and fired, it shows a grass green color, which is a chrome green glaze.
The meaning of basic glaze
Generally speaking, there are many ways to explain the meaning of "glaze", or to explain the composition of "glaze", and to label the ingredients of "glaze". And what is a basic glaze? Simply put, it is a mixture of oxidizing raw materials (including carbonate) that does not contain colorants and is covered on the surface of the ceramic work before it is fired. These mixed oxidizing raw materials, whether they are lime glaze or raw materials containing barium, zinc, magnesium, and other alkaline ingredients, can appear milky, transparent, runny, matte, or undercooked after being fired at high temperatures. state; these different mixtures constitute the basic glaze.
Classification and composition of basic glazes
According to the composition of basic glazes, basic glazes can be divided into lime glaze, lime barium glaze, lime zinc glaze, lime magnesium glaze, lime barium glaze Zinc glaze, lime barium magnesium glaze, lime zinc magnesium glaze, lime barium zinc magnesium glaze, etc., and due to the amount of potassium oxide and sodium oxide contained in the glaze, the glaze style has different combinations and changes. The following two groups are listed below: Example to illustrate.
1. Lime glaze: (Glaze formula is converted into weight percentage, the fired test piece is shown in Figure 1)
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.8
2. Lime barium glaze: (Glaze formula is converted into weight percentage, the fired test piece is shown in Figure 2)
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.45
BaO 0.35
3. Lime zinc glaze: (Glaze formula is converted into weight percentage, the fired test piece is shown in Figure 3)
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.4
ZnO 0.4
4. Lime magnesium glaze: (Glaze formula is converted into weight percentage, the fired test piece is shown in Figure 4)
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.4
MgO 0.4
5. Lime barium zinc glaze: (Glaze formula is converted into weight percentage, the fired test piece is shown in Figure 5)
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5CaO 0.4
BaO 0.2
ZnO 0.2
6. Lime barium magnesium glaze: (Glaze formula is converted into weight percentage, the fired test piece is shown in Figure 6)
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.4
p>BaO 0.2
MgO 0.2
7. Lime zinc magnesium glaze:
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.4
ZnO 0.2
MgO 0.2< /p>
8． Lime barium zinc magnesium glaze:
KNaO 0.2 Al2O3 0.25~0.45 SiO2 2~5.5
CaO 0.2
BaO 0.2
ZnO 0.2
MgO 0.2
Two-1 lime glaze:
KNaO 0.3 Al2O3 0.35~0.55 SiO2 2~5.5
CaO 0.7
p>
2. Lime barium glaze:
KNaO 0.3 Al2O3 0.35~0.55 SiO2 2~5.5
CaO 0.4
BaO 0.3
Two-3. Lime zinc glaze:
KNaO 0.3Al2O3 0.35~0.55SiO2 2~5.5
CaO 0.4
ZnO 0.3
Two-4 lime magnesium glaze:
KNaO 0.3 Al2O3 0.25~0.45 SiO2 2~5.5
CaO
0.4
MgO 0.3
Di-5 lime barium zinc glaze:
KNaO 0.3 Al2O3 0.35~0.55 SiO2 2~5.5
CaO 0.3
BaO 0.2
ZnO 0.2
Di-6 lime barium magnesium glaze:
KNaO 0.3 Al2O3 0.35~0.55 SiO2 2~ 5.5
CaO 0.3
BaO 0.2
MgO 0.2
Di-7 lime zinc magnesium glaze:
KNaO 0.3 Al2O3 0.35~0.55 SiO2 2~5.5
CaO 0.3
ZnO 0.2
MgO 0.2
Di-8 lime barium zinc Magnesium glaze:
KNaO 0.3 Al2O3 0.35~0.55 SiO2 2~5.5
CaO 0.2
BaO 0.2
ZnO 0.15
MgO 0.15
Characteristics and selection of basic glazes
There are different types of alkaline components in basic glazes. In addition to changing the melting temperature of the glaze and making the glaze appear milky, In addition to the appearance phenomena of glazes such as turbidity, transparency, and mattness, it is also a condition that promotes the ideal color of the color agent. For example: lime glaze can make 1% cobalt oxide turn blue, but lime magnesium glaze can make 1% cobalt oxide turn purple-blue or even purple. Lime zinc glaze makes chromium oxide gray and lime barium glaze makes chromium oxide dark green. Therefore, in order to produce a bright dark green glaze color under oxidation firing conditions, lime glaze and lime barium glaze must be the ideal basic glaze selection conditions.
The following four experiments respectively used six kinds of lime glazes (Figure 7), lime barium glaze (Figure 8), lime zinc glaze (Figure 9), and lime magnesium glaze (Figure 10) with different acid ratios. ) with five different sets of color-developing agents, namely 1% cobalt oxide, 5% copper carbonate, 5% iron oxide, 10% iron oxide, 10% iron oxide and 10% ashes . From the above experiments, the characteristics of different types of basic glazes can be compared.
For some specific glaze colors, the choice of basic glaze categories needs to be even more careful. For example, the common bright iron red glaze color agent uses 15%~18% red iron oxide and 10%~15% bone ash as the color development condition (black iron oxide and calcium phosphate can also be used), and under low aluminum oxide (raw material (Less than 10% kaolin), the acid ratio of alumina and silica is between 1:7 and 1:10, which is the best neutral acid state. The best choice for its basic glaze is lime magnesium glaze, and its range is 0.2 mol ~ 0.3 mol, the others are lime glaze, lime barium glaze (0.1 mol), lime zinc glaze. However, the ultra-high 0.1 mole (weight percentage of about 2% to 3%) zinc oxide in the lime zinc glaze prevents the iron oxide from developing a bright red color and appears earthy yellow.