| Glaze color is the soul of ancient ceramics’ scientific connotation and artistic style.The formation and color of its glaze is an essential link in recognizing the scientific and artistic value of ancient porcelain.Generally speaking,the composition of the glaze(especially the types,sources and contents of coloring elements,etc.)and the structure of the glaze layer(including bubbles,microcrystals and phased structures,etc.)are the two critical factors that affect the glaze color and appearance texture.Firing and processing technologies also have an essential impact on the glaze color and texture.Accordingly,three different types of glazes of Jingdezhen bluish white porcelain glaze(monochrome glaze),iron crystal glaze(crystalline glaze)and imitation Song dynasty Jun porcelain(kiln-changing glaze)were selected as the objects of study.Analysis and study were carried out using spectrophotometer,X-ray fluorescence spectroscopy(XRF),ultra depth of field microscope,electron scanning microscope(SEM),etc.The influence of elemental composition and structural changes on glaze color during firing was studied,and the formation process and color mechanism of different types of glaze colors were explored.The main research contents and results are as follows:(1)Bluish white porcelain in Jingdezhen was selected for color analysis,the microstructure and chemical composition of the samples were taken at different firing temperatures.The results of the analysis show that the changes in ceramic glaze color,chemical composition and microscopic bubbles are closely related to the firing temperature.In the firing process,as the firing temperature was increased,the glass texture of the glaze was gradually enhanced,and the glaze color gradually changed from pink to pale yellow and then slowly showed a pale to dark blue-white color.It was found that in the firing temperature reached the range of 1200℃-1240℃,small bubbles appeared in the glaze layer an average of approximately 0.17 mm,improving the scattering of the incident light,and the glaze showed a gentle and soft milky feeling;When the firing temperature at 1300℃,the average bubble size increases to 0.48 mm,and the bubbles of this size scale are more conducive to light passing through,this improves the glass texture of the glaze,as well as improving transparency.Secondly,during the firing process,the molten glaze leaches into the solid tires,prompting the migration of K2O,CaO,Na2O and MgO in the glaze layer and the enrichment of impurity elements(including coloring elements such as iron)around the bubbles in their phase boundaries,causing the glaze layer to form an uneven distribution.As the further increase of firing temperature,bubbles will escape,other light elements will volatilize,the concentration of coloring elements increases,and the glaze layer shows a gradually deepening cyan color under the reducing atmosphere.Chemical composition analysis revealed that the elemental content of the glaze varied significantly at different firing temperatures.Exploring the relationship between the change of glaze element content and firing temperature is important for studying the firing process and tracing the original recipe of ancient ceramics.(2)The crystalline glaze of the iron series was studied,and the triangular batching method was used to analyze and study the migration of the glaze elements in their composition and thermal process.It was found that the glaze layer "boiled"at 1200℃ due to the production of a large number of bubbles during the heating process and gradually crystallized around the bubbles during the cooling process to form oil droplet-like red markings.By analyzing the color,microstructure and chemical composition of the sample,it can be seen that the formation process of oil drop spots is attributed to the decomposition of iron oxide at high temperatures,releasing a large amount of gas,causing the glaze layer to blister and transporting Fe in the glaze layer to the surface during the bubble escape process,when a large amount of iron oxide is deposited on the glaze,the scattering and internal friction of the incident light is increased,and the glaze is black;At the crackling of the glaze bubble during cooling,supersaturated iron oxide crystallizes in the glaze to form a large number of hematite dendritic crystals,which are macroscopically manifested as red oil droplet-like markings.(3)Taking the imitation of traditional Jun porcelain as the research object,the relationship between the migration of glaze elements and the formation of glaze color and markings during the heat process of kiln-changing glaze was studied.During the firing process,it was found that the glaze color changed from red to yellow to gray and then blue,finally showing a changeable red-blue-white color.At 1250℃,fine bubbles were observed to appear on the glaze,and the micro structure is a nano-mesh structure.With the increase in firing temperature,the bubbles grew,and the size of the nano-mesh splitting structure increased from 30 nm to 113.16 nm,forming a faint blue light,and the glaze color changed to blue-green.Due to the migration of elements during the firing process,when the firing temperature reaches 1300℃,the Si/Al ratio in the glaze is higher than 11,which is conducive to the formation of split-phase droplets,and the increased Fe3+O-Fe2+and Fe2+ in the glaze show blue-green,emerald green like jade.After cooling with the furnace,bubbles in the glaze layer carry the red Cu nanospheres to the surface during the rising process and play the role of stirring the glaze layer during the movement;In addition,there are rich microstructures such as nanonetwork structure,split phase droplets and residual quartz crystals in the glaze layer,and the average size of the structure is greater than the wavelength of incident light(100 nm),which can occur Mie scattering to give the glaze layer appear milky white and make the glaze color softer.At high temperatures,the viscosity of the glaze melt decreases and flows downwards under gravity,and macroscopically,the surface of the glaze shows fluid colored stripes.(4)Analyzed the formation of glaze color differentiation during glaze firing for bluish white porcelain,iron-based crystalline glaze and Jun porcelain reveals that the color presentation of bluish white porcelain glaze is mainly derived from the color development of Fe2+.The appearance of tiny,dense bubbles in the glaze layer at 1240℃ increases the emulsification of the glaze,giving it a uniform color.Compared to the bluish white porcelain,the glaze of Jun porcelain contains higher amounts of K2O,CaO,and P2O5,so the glaze layer is easy to melt and flow and the microstructure is complex,which makes the color of Jun porcelain glaze tend to blue,with a mottled or flowing texture.Given the high iron content(5 wt%-8 wt%)in the iron crystalline glaze,the decomposition of the glaze layer at high temperatures results in the phenomenon of boiling and bubbling,and the precipitation of dendritic crystals after the escape of bubbles is the main reason for the formation and coloring of crystals in the glaze. |
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