It is about the frit lustrous colourless glazes with the content of PbO 10-60% of the mass. With regards to such a high content of the lead, they are recommended for the production of decorative ceramics entirely.
The glazes are designed for the firing temperatures of 920-1000°C, whereas it is possible to burn some of them in thin layer till 1100°C. At temperatures higher, it is the danger of partial dissolving of body mass in the glaze or of the percolatin of the glaze to the body.
The glazes are suitable for the coloured burnt body above all, whose coloration they emphasize. They show out the bright luster and high transparency, that is the reason why they are ideal for the application on underglaze decoration, e.g. by coloured engobes, pigments or salts.
With regard to high thermal expansivity on most of bodies, they crackle, that is the reason why they are recommended to apply on such body mass, whose thermal expansivity coefficient is a > 705 x 10-7K-1.
It is possible very well to engrain the glazes by colour oxides and by ceramic pigments to intensive shade in using 4-8% of mass pigments. They are suitable for the preparation of majolica colours also.