Published online by Cambridge University Press: 02 January 2018
Ultramarine pigments were synthesized successfully from Na-A zeolite derived from kaolin waste. Na-A zeolite encapsulates the sulfur species formed and which act as chromophores, which circumvents their oxidation and the subsequent liberation of high levels of toxic gases during the reaction. Different Na-A zeolite matrices with various grain sizes (fine to coarse) were mixed with sulfur and sodium carbonate in various proportions to study the influence of these variables on the pigments’ colours and hues. After calcination at 500°C for 5 h, the products were characterized by X-ray diffraction, X-ray fluorescence and Raman spectroscopy and were classified by the Munsell system (colour and hue). Products with colour ranging from blue to green with various hues were obtained. Both colour and hue were affected by the amount of additives and by the particle size.