Display 14 bone China defects

8, crystallization of bone porcelain glaze and the matt meaning: bone porcelain glaze and glass, as the composition of the chemical composition, sintering temperature, sintering time and the cooling time, has a tendency to spontaneous crystallization. But it did not according to the wishes of the people, when bone porcelain decoration without crystallization or not in the specified area precipitation ideal crystal flower of crystalline glaze, but irregular dense crystallization, the bone porcelain glaze devitrification, which affect artistic effect. The reason: 1) Glaze decoration bone China products, in addition to the transparent glaze is close to the amorphous vitreous, many types of bone porcelain glaze contain different crystal shape size. Bone China opacified glaze in the grain size of about 1 - 3 microns or more fine bone China grain of mat glaze is a opacified glaze grain big 5 - 6 times, but still small, examines the naked eye can not, only the gold dust glaze has a visible suspended grain. According to Thai, theory of crystallization, melt crystallization must first hypersaturated state into crystalline material, in order to form crystal nucleus cooled, followed by the body must be within the crystallization temperature range of the material for heat preservation, in order to make crystal nucleus development growth. And the different choices of different thermal insulation and heat preservation time, and can control the size and shape of the crystal flower. As shown in figure 6 - As shown in figure 1 liquid and crystallization process, : melt only precipitation in the two curves intersect crystal, melt in close to T. Slow temperature insulation cold, can get a small amount of big crystal, in the second line intersection point of the corresponding temperature insulation crystal dense make and devitrification light. ( 2) Bone porcelain glaze composition, there are a lot of not easy to melt the inert material, silica (such as: Sio) , calcium oxide ( Ca0) Baryta ( BaO) And magnesium oxide ( MgO) , tin oxide ( SnO2) , 3 oxidation 2 aluminium ( A1202) , chrome oxide ( CR2O3) And calcium phosphate ( Ca2 ( PO2) 2) And spinel etc. , especially when they are in bone porcelain body surface, will lead to matt dark hysteresis dull color, Ro and R2 are of low atomic weight elements can make magnesium, zinc oxide, and boron although atomic weight low potassium crystals and make bone porcelain glaze has the strong ability of crystallization. Such as: sodium ceramic glaze of liquidity but it can only be strengthened, and unfavorable to the crystallization of bone porcelain glaze. Some high atomic weight element oxide, adverse bone porcelain glaze knot products such as: barium ( Ba) , lead ( Pb) And so on. Bone porcelain glaze composition of SiO2 with RO molecular ratio & lt; 3. Crystallization tendency particularly strong. For example SiO2, R0 & gt; 2. 5 and & lt; 3, still have a tendency to crystallization. If SiO2 and lead oxide ( Pb0) The ratio of the small, also can produce matt and not familiar phenomenon, if A1203 content is too high, are particularly sensitive to burn into the cooling speed, then affects bone porcelain glaze gloss. All of the alkaline substances in the glaze is more or less volatile ( Except for the lead glaze) , bone porcelain glaze layer such as these, after calcination will lose its luster. ( 3) Bone porcelain glaze layer is too thin or too in the body, glazing, bone porcelain slurries did not stir well, this will make bone China products lose luster after firing. ( 4) Glaze layer tray, sagger wall without coating, near the box wall parts, due to the volatilization of bone porcelain glaze easy melt components appear light. ( 5) Sintering temperature is too low, the bone China products because owe to burn, the bone porcelain glaze illiquid and lose luster, even can't see the flowers. Due to bone porcelain glaze firing tend to natural crystallization, can produce devitrified phenomenon, thus and matt structure, the so-called (devitrification Bereft of glass transparent nature) 。 — Tangshan bone porcelain gifts to be continued. 。 。 。 。 。