Brief description of the technological process of porcelain souvenirs manufacture
The primary model is shaped by the sculptor from clay or sculpture plasticine, but in the manufacture we use flexible silicone model.
According to this model we manufacture accessories for replication of gypsum forms and gypsum forms themselves, consisting of several pieces (3 to 8 or more, depending on the complexity of the model).
Molding porcelain mass (slurry) is prepared by wet milling of Spain production porcelain mass with glass balls in ball mills. The composition of the slurry includes high quality white fireclay, kaolin, quartz, feldspar and some rheological additives.
Porcelain mass is poured into dry gypsum forms. A few minutes after pouring, when the water is absorbed in the form and on its inner surface there appear a layer of compacted mass- moulding, excess liquid is drained. Some complex products are bonded by porcelain mass of several mouldings.
Fabricated intermediates are dried, seams are cut, the surface is treated manually using a wet sponge.
This is followed by a preliminary firing at 800° C in an electric furnace. After this the intermediates lose their ability to soaking in water, remaining porous.
After preliminary firing the models are painted with special underglaze paints based on metal oxides and with salt solutions by hand or airbrush. Then the models are glazed by dipping in a suspension of lead-free glaze. The glaze suspension is a mixture of fine ground glass-forming components: quartz, pegmatite, chalk, dolomite, etc. in water.
The composition of the glaze is perfectly matched in accordance with the thermal expansion of the crock and its sintering temperature, as well as provides maximum shine and bottling without crystallization.
The final firing is carried out in electric furnaces made by German company Helmut Rohde Gmbh at 1200 ° C. During this firing the sintering of models took place with shrinking of the geometric dimensions about 8-9%, but the finished products lose almost 15% of the original model’s size. Products become non-porous, acquire hardness, translucency, and other properties that characterize porcelain.
This is followed by sorting, identifying of defective items and wrapping.
Since the production of artistic ceramic products with complex shapes today defies automation at a reasonable cost (except for the automatic control of firing), the proportion of manual labor is 70-80%. The entire production cycle starting with the manufacture of gypsum forms is from 10 to 15 days, if mouldings are available - from 5 to 10 days.