Nevertheless, the presented results show clearly that sodium polysulfides can be useful substrate for conventional ultramarine production. The further industrial experiments are required to optimize the procedure. A impregnation with various polysulfides, followed by calcination depends on number of sulfur atoms in the polysulfide molecule. . The polysulfides S 3 and S 6 seem to be the most effective precursors for generation the S 3- radicals and they provide the most intense blue color of the products. . Modification with elemental sulfur results in almost colorless product of unknown structure. .
Sodium sulfide allows to obtain light blue product of prevailing cristobalite structure.
The ESR spectrum of this sample indicate some anisotropy. The optimization of hydrothermal crystallization of sodalite in the presence of sulfur compounds do not lead to the products of deep blue color. . It has been found that sodium thiosulfate can be applied as radical precursor although the color of the product is also not intense. . It remains still not clear whether the hydrothermal synthesis of sodalite with sulfur compounds is able to incorporate a sufficient amount of sulfur to provide the intense blue coloration of the final products. Industrial experiments on thermal synthesis with sodium polysulfide instead of elemental sulfur resulted in blue products of similar properties as conventionally obtained ultramarine. .