In the firing process of ceramic bone china cups, the smoothness of the glaze surface is one of the core indicators determining product quality. Its control requires a comprehensive approach from multiple dimensions, including raw material selection, process optimization, firing regime, and equipment adaptation. Among these, glaze formulation, glazing technique, firing curve, and kiln environment are key control points.
The glaze formulation is the foundation of a smooth glaze surface. Ceramic bone china cups typically use frit glazes, the composition of which must match the coefficient of thermal expansion of the body to avoid glaze cracking or peeling due to thermal stress. The particle size of raw materials such as quartz and feldspar in the formulation must be controlled; too coarse a particle size easily produces bubbles, while too fine a particle size results in poor fluidity. At the same time, adding an appropriate amount of talc can improve the suspension of the glaze slurry and reduce sedimentation, while fluxes such as zinc oxide can lower the melting temperature of the glaze and promote uniform spreading in the molten state. Furthermore, volatile or impurity-containing raw materials should be avoided in the glaze to prevent pinholes or discoloration during firing.
The glazing process directly affects the thickness and uniformity of the glaze layer. Ceramic bone china cups often use dipping or spraying methods. During glazing, the density of the glaze slurry must be controlled within a reasonable range. Excessive density leads to an overly thick glaze layer, resulting in uneven shrinkage during firing; insufficient density results in a thin glaze layer with insufficient coverage. During spray glazing, the spray gun pressure, glaze flow rate, and body rotation speed must be adjusted to ensure uniform glaze adhesion. For irregularly shaped cups, manual glazing or localized spraying can be used, but the operation method must be strictly controlled to avoid artificial marks. After glazing, the cup must be allowed to dry completely to prevent glaze flow and localized accumulation.
The firing process is crucial for a smooth glaze surface. Ceramic Bone China cups typically employ a two-stage firing method: high-temperature bisque firing and low-temperature glaze firing. During bisque firing, moisture and organic matter in the body must be thoroughly removed to prevent glaze defects caused by gas evaporation during glaze firing. During glaze firing, a suitable temperature profile must be established: the oxidation stage must fully remove crystalline water and organic matter from the glaze; the high-temperature stage must maintain a stable atmosphere to avoid a reducing atmosphere that would darken the glaze color; and the cooling stage must involve slow cooling to prevent cracks or deformation due to thermal stress. Furthermore, the kiln pressure regime must be matched with the temperature regime to ensure the glaze spreads evenly in a molten state.
The kiln environment has a significant impact on the smoothness of the glaze surface. Roller kilns or pusher kilns, due to their good temperature uniformity, are suitable for mass production of ceramic bone china cups. During firing, the kiln atmosphere must be controlled; an oxidizing atmosphere promotes full melting of the glaze, while a neutral atmosphere reduces glaze oxidation and discoloration. Simultaneously, the kiln temperature sensor and spray gun must be checked regularly to ensure the accuracy of temperature and atmosphere. For irregularly shaped or large-sized cups, nail firing or hanging firing processes can be used to reduce the contact area with kiln furniture and avoid glaze adhesion or deformation.
Body preparation is a prerequisite for a smooth glaze surface. The bodies of ceramic bone china cups require meticulous trimming to ensure a smooth, crack-free surface. The trimming force must be controlled to avoid reducing the body's strength due to excessive polishing. In addition, the body must dry evenly to prevent uneven shrinkage during firing due to localized differences in moisture content. For thin-walled cups, a wet repair process can be used, where repairs are made while the body is semi-dry to reduce drying cracks.
The exterior decoration must be optimized in conjunction with the smoothness of the glaze. Ceramic Bone China cups often employ underglaze or in-glaze decoration techniques, requiring careful consideration of the compatibility between the pigments and glazes. The pigment particle size must match the glaze; too coarse a particle will create a grainy appearance, while too fine a particle will affect the color development. After decoration, a low-temperature firing process is necessary, with strict temperature control to prevent discoloration or pigment evaporation due to excessive heat.
Quality inspection is the final guarantee for a smooth glaze. After firing, the ceramic bone China cup undergoes rigorous inspection, including visual inspection, gloss measurement, and smoothness testing. Minor defects can be repaired using polishing or acid washing, but the intensity must be controlled to avoid damaging the glaze. Finished products must meet relevant standards, such as a smooth, unblemished, bubble-free, and crack-free glaze, ensuring product quality.
