The traditional starting reagent for the synthesis of ultramarine blue, namely kaolin, has to be heated before the synthesis to weaken the structure of the kaolin. Two batches of fine fly ash (an aluminosilicate waste product from the combustion of coal) were successfully used to synthesize ultramarine blue. Infrared, Raman and X-ray diffraction results confirmed the formation of the product. Fly ash has the advantage over kaolin of being amorphous. The results further showed that the transition from the green ultramarine species to the blue species coincided with an increase in the ratio of the amount of S-3(-) species relative to the amount of S-2(-) species. (C) 2004 Elsevier Ltd. All rights reserved.