The aventurine glazes are frit, hard alkaline, coloured opaque glazes without the content of PbO. They are designed for the firing temperatures of 960-1080°C. By the temperatures over 1000°C, they flow off very hard.
They are characterized by highly effective resplendent crystals, by which is the layer of burnt out glaze marbled. This effrect is caused by the supersaturation of the glaze with iron oxide, that comes out from the molten glass at cooling in the form of crystals.
The glazes are health unexceptionable and so applicable to production of kitchenware. As a rule, they are used for the decorative ceramict, because they crackle very hardby reason of theirs hight thermal expansivity coefficient a > 90-120.10-7 K-1. In longer contact with the water (vases, flowerpots), they appear round of the cracks the white advance growth of deposit alkalis.
The aventurines are the glazes very few reliable in reproducibility. They demand optimal conditions for the firing. Above all, strong layer of teh glaze, the firing in horizontal position and preferably long hardening, because the crystallization demands definite time. At the firing in vertical position, they flow off very hard and the crystals are formed in the underlay, where the thicker layer of the glaze cumulates. It is possible to reach good effects at the underlay by white glaze). They are suitable for all glazing techniques.