Fe2O3 içeren hammaddenin şeffaf sırı renklendirme etkisi

Ceramic body, engobe and glaze are coloured with pigments that are classified as natural and synthetic. Natural pigments exist as simple oxides in nature. It draws attention in particular iron oxides, which can give different colours among natural pigments. The main raw material of traditional pottery is red clay which includes iron oxide and a wide range of researches are performed studies on the use of red clay for colouring ceramic casting slip, engobe and glaze. In this study, colouration of transparent glaze maturing at low temperatures was intended by adding the raw material containing Fe2O3 from Cavdarusagi village in the region Kayseri-Yahyali as a natural pigment. The raw material was wet ground in a ball mill for 30 minutes and passed through a 100 μm sieve. Chemical analysis of undersize raw material contains 6.86 wt. % Fe2O3 which was determined by X-ray fluorescence spectrometer XRF-Rigaku ZSX Primus. Undersize raw material was dried at 110 °C and added into standard transparent glaze at 20 wt. %, 40 wt. % and 60 wt. %, respectively. Glazed samples were fired at 1000 °C in a laboratory kiln (Refsan Kaleo- 27). Performing colour measurement of glazed samples, L *, a *, b * values were determined. Formation of new phases was examined by X-ray diffraction (XRD), development of the microstructure was determined by scanning electron microscopy (SEM). Glazed samples’ L*, a*, b* values were measured by Minolta CM-3600d color measuring instrument. The L* value, representing lightness or darkness of the colour, decreased due to the increment of the additional raw material amount and allowed the darkening of the colour. The lowest L * value (39.44) was measured for glaze with the 60 wt. % additional raw material compared with standard and other additive containing glazes. The a* value is expressing redness when it is positive. A small increment in the a* value was seen due to the increment of the additional raw material amount in glaze. The b* value is expressing yellowness when it is positive. The lowest amount (20 wt. %) additional raw material containing glaze has the highest b* value (+18.18). Due to the increasing amounts of additional raw material, colour changed from light brown to dark brown. The crystalline phase analysis of the prepared glazes was determined by Rigaku Rint 2200 (XRD) device. SiO2 phase was identified in all glazes fired at 1000 °C. In addition to SiO2 phase, anorthite phase was detected when the amount of additional raw material was above 40 wt. %. The microstructure of the prepared glazes was performed by Zeiss the EVO 50 EP scanning electron microscope (SEM). Representative back scattered electron (BSE) image for glaze containing 60 wt. % additional raw material revealed that the crystals formed in the glassy phase. According to the results of the SEM-EDX (Energy Dispersive X-ray) analysis of the same sample, anorthite containing glassy phase region contained 57.46 wt. % SiO2, 26.20 wt. % Al2O3, 10.93 wt. % CaO, 2.75 wt. % Na2O, 1.41 wt. % MgO, and 1.25 wt. % K2O. These results revealed the existence of the anorthite phase was determined by the XRD device. The other phase was SiO2 which detected by XRD device. According to another EDX result, 100 wt. % SiO2 was detected in the microstructure. In addition, Fe2O3 grains were identified with microstructure analysis. The grains were not dissolved in the glassy phase and have played an effective role in the formation of colour with staying insoluble.