Some color aspects of Parian bodies

Abstract

The two coloring oxides, CoO and NiO were included separately in a self-glazed parian body ⪡highly feldspathic porcelain⪢ in 5 different concentration between 1 and 10 wt%. The host body consisted of 75% feldspar and 25% kaolin. The mixes were pressed and matured between 1125°C and 1150°C. The produced colors were characterized visually as well as in reference to the CIE system. The densification of the blue and green bodies were slightly reduced, although higher density values were achieved. This was attributed to the effect of the Co 2+ or Ni 2+ dense aluminate or silicate. However, their influence was counter balanced by the enhanced leucite formation and higher porosity glassy phase. Various shades of blue were obtained by introducing Co 2+ . Maximum difference in color Δ E = 12.97 Judds was obtained by incorporating 5 wt % and firing at 1125°C while a value of 11.69 Judds was obtained upon firing a specimen with only 1 wt % at 1150°C. The latter value is comparable to that obtained by incorporating 10% of blue stain. Ni 2+ produced various shades of green with a maximum of Δ E = 5.44 Judds upon firing a sample with 5 wt % at 1150°C. The results are discussed in view of the ligand field theory as well as X-ray diffraction analysis.