Minerals and Metals in Ancient India v1.c26.s6.t3.8

v1.c26.s6.t3.8

would minimize the chance of zinc vapour getting trapped in any one part of the retort and forcing that part to burst open. Little bit of the glassy phase helped in sintering by acting as skeletal adhesive; 0.7 per cent chlorine in the residue glass, with 7.13 per cent Na₂O (column 2 in Table 18.2) is probably close to saturation. (Freestone *et al.*, 1985a: 237) Secondly, soda vapour would react with the silica and alumina of the clay in the interior surface of the retort wall to produce a thin film of glaze. This glaze would prevent the loss of zinc vapour through the micropores in the thin clay wall of the retort. (Hegde, 1989: 92) The low level of lead oxide (1.72 %, *vide* column 5 in Table 18.2, also 18.3 and 18.4)