Controllable Preparation And Decorative Effect Of Iron-based Crystalline Glazes

As a country with the longest history of porcelain manufacture,China has a rich ceramic culture.The integration of porcelains in different periods with the social,cultural,and technological factors of the time can often result in many new forms of artistic decoration.Celadon tended to mature in the Eastern Han Dynasty,a pattern of"celadon in the south and white porcelain in the north”was formed by the Sui and Tang Dynasties.Since the Song Dynasty,a series of colorful high-temperature glazes have appeared.Jun glaze combines the chemical and physical colors perfectly,showing the gorgeous effects such as bluish-green,sky-blue,eggplant-violet,blood-red and so on.The precious iron glazes such as“Yao Bian,oil-spot,hare's fur”of Jian kiln tea bowls,and the double-glazing products such as“tortoiseshell,tiger stripe,hare's fur”of Jizhou kiln tea bowls are also world-famous.By the Qing Dynasty,the preparation technology of all kinds of overglaze color,underglaze color,mixed color,low-temperature glaze and high-temperature glaze reached the peak,so that a variety of porcelain decorative categories with a high level in arts and crafts were invented and become prosperous.Archaeometry research reveals the scientific regularities contained in the archaeological ceramic samples on the basis of scientific cognition,and the original intention of this study is to further carry out the practice of“making the past serve the present”by learning from the scientific regularities obtained from the archaeometry researches.Based on the ancient black glazes composition system,the Si O₂-Al₂O₃-K₂O-Mg O-Ca O-Fe₂O₃?-CoO/CuO?multi system high-temperature glazes were designed and controllably prepared.Glazes with different decorative effects can be obtained by modifying the firing schedules to control the crystallization behavior and microstructure of the glazes.In addition,the crystallization regularities and coloring mechanism of the glazes with different firing schedules are discussed,which provides theoretical basis for further understanding the science inside ancient black glazed porcelains,and also provides scientific and technical basis for the preparation and innovation of modern porcelains.The experimental results are as follows.1)The samples of series KL,obtained by opening the furnace for quick cooling,show black glazes with a large amount of leaf-shaped or snowflake-shaped?-Fe₂O₃ crystals precipitated on the glaze surface,which appear to be shiny silvery speckles under the naked eye observation,looking like the stars in the night sky.Moreover,the high degree of undercooling of Fe leads to the bulk crystallization of flaky?-Fe₂O₃ with a scale of 3?5?m within glaze layer.Under the irradiation of light,the glaze shows the effect of golden stars shining.2)The samples of series SL,cooled with the furnace after power off,show yellowish brown glazes with matte rims,which are caused by the surface crystallization of densely arranged dendritic?-Fe₂O₃.A large number of silvery speckles scattered on the surface of the yellowish brown crystallization layer are crystalline aggregates of?-Fe₂O₃.3)The combined influence of the high temperature viscosity characteristics of the glaze and the inclined belly wall of the bowl lead to the flowing of the glaze during firing,which results in the difference of glaze thickness and the variation of Fe enrichment at different thickness positions,thus making the rim,the wall and the bottom of the bowl show different artistic effects.The silvery speckles on the bowl wall are composed of snowflake-shaped and leaf-shaped?-Fe₂O₃ aggregates,and the silvery thin layer on the inner bottom of the bowl is formed by the precipitation of a large number of granular?-Fe₂O₃crystals.4)The?-Fe₂O₃ crystals on the surface of the bowl wall and on the inner bottom of the bowl both appear bright silvery.This is because that the arrangement of?-Fe₂O₃ has good orientation,and it can reflect the visible light in the full band.When the physical coloration caused by the structural arrangement plays a leading role,the chemical coloration of Fe³⁺is inhibited,and the macroscopic color appears silvery.5)During the firing process,?-Fe₂O₃ experiences“crystallization-remelting-secondary crystallization”,which depends on the super-saturation of the glaze melt.In a weakly oxidizing atmosphere,dendritic?-Fe₂O₃ crystals are precipitated at about 1000?1050?.6)The substitution of a small amount of CoO/CuO for part of Fe₂O₃ can effectively control the crystallization behavior and microstructure of the glaze,and the main precipitated crystals on the glaze surface are Co_xFe_3-xO₄/Cu Fe₂O₄,thereby obtaining unique artistic effects.