Fig. 7. XRD patterns of Pr–zircon pigments.
3.2.3. Pr–zircon yellow pigments
Table 3 reports the L*a*b* values of the Pr–zircon pigments.
The yield of yellow colour is described by the value of the
b* parameter, more positive b* values corresponding to more
intense colour hues. Although pigments prepared with decomposed
product are characterised by high brightness (L* value),
better yellow colour appearance with higher b* values was
obtained. In addition, reflectance curves of glazes containing
pigment prepared with decomposed products closely matches
with the commercial pigments (Fig. 3).
Fig. 7 reports the comparison between the XRD patterns
of Pr-containing zircon pigments. In the prepared pigments,
additional Pr8Si6O24 and m-ZrO2 phases were observed in comparison
to the commercial pigment. Although, it is well known
that praseodymium oxide is generally assumed to form a solid
solution with the zircon lattice, solid solution reactions between
zircon and Pr compounds were not completed and Pr compound
reacted with SiO2 to form Pr8Si6O24. However, effect of this
phase on the colour properties were not determined but a previous
study reported that praseodymium oxide may impart a
greenish yellow colour because the colouring component is not
fully incorporated into the zircon lattice