Study On High Temperature Copper Red Glaze

For the purpose of exploring the influence of compositions and valence states on the color generation of copper red glazes,firstly,preliminary studies and experiments on firing schedules and ingredients of high temperature copper red glazes were carried out to find the main factors contributing to the color of copper red glazes.The optimum recipe of copper red glaze was formulated.Secondly,orthogonal experimental method was employed to optimize the copper red glaze.On the basis of optimized recipe,effects of Si/Ca,Si/Al,Cu/Sn,amount of calcium phosphate addition and concentration of reducing atmosphere on color of copper red glazes were investigated.XPS was used to interrogate the valence states of copper in the glazes.The gloss and coloration effects of copper red glazes were also characterized by using colorimetry measurement and vancometer.SEM and EDS were employed to characterize the microstructure and elements of the glazes.The optimum recipe for the copper red glaze is as follows:quartz 40%,kaolin 7%,calcium carbonate 20%,copper oxide 0.5%,tin oxide 2.5%,Na-feldspar 24%,K-feldspar 10%.The optimized glaze exhibit a bright red color with good uniformity and slight crackles and high fluidity can be attained when fired at high temperatures.Chroma parameter values are as follows:L*=82.5,a*=22.35,b*=4.64.Results of composition effects show that when Si/Ca ratio is 3.69,hue of the glaze turns to be purple blue with its a*and b*value being 19.72 and-11.61,respectively.Such recipe is situable for copper fancy glazes.While Si/Ca ratio is 4.81,the max a*value is 21.10,b*is 7.22,with which the glaze is of deep red colour and high gloss.When Si/Al ratio is 12.16,a*value is the maximum 26.93 with its glaze effects being bright red color,slight crackles which is suitable for Lang red glaze.When Cu/Sn ratio is 1.39,the max a*value is 22.93 with dull red and good gloss which is suitable to produce Jun red glaze.a*and b*values primarily decreases with the increasing of calcium phosphate addition.When its additive amount is 0.6%,hue of the glaze turns to be purple blue with which the a*and b*value is-0.04 and-11.42,respectively.While the additive amount is 0.8%,a*and b*value is-1.13 and-15.32 with a deeper blue hue.An optimized firing schedule of copper red glaze is as follow:property of fire changing temperature is 960?,concentration of CO during high reducing period(960?-1180?)is 3%-9%.While concentration of CO during weak reducing period(1180?-1280?)is below 2%.Coloration effects of the glaze are of bright color,high gloss and good fluidity.When concentration of CO during the two periods is above 10%and 3%,hues of the glazes will turn dull red or black due to heavy reducing atmosphere.The results of XPS indicate that states of copper existence in red glaze are Cu2O,CuO and Cu.Apparent hues of the glaze turn deep red when the relative amount of zero valent copper increases.While hues of the glaze become bright red when the amount of univalent copper increases.States of copper existence in bright red glaze are Cu2O,CuO and small amount of Cu.When the state of copper existence is CuSiO3,glaze can appear blue hue.