Minerals and Metals in Ancient India v1.c11.s14: Glaze/Vitreous Paste
Minerals and Metals in Ancient India v1.c11.s14
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Glaze/Vitreous Paste
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Allied to faience was a hard vitreous paste made by mixing glaze with a siliceous powder and firing at a high temperature. So this paste resembles glass in some respects. Occasionally beads of this material were fired at too great a heat with the result that they lost their exterior glaze and had a dull and pitted surface. Owing to their containing so much glaze, beads of this material have in general retained their colour much better than the faience beads. Beads of this vitreous paste were made throughout the occupation of Mohenjo-Daro. It has a smooth fracture and shows no evident impurities or admixture as would be the case if a paste had been mixed with an ordinary adhesive to strengthen it.
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Sana Ullah analysed one of the samples:
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| Silica | 88.12 per cent |
| Alumina | 3. 2 per cent |
| Ferric oxide | 1.82 per cent |
| Calcium oxide | 1.26 per cent |
| Alkali oxide | 5.04 per cent |
| Cupric oxide | 0.46 per cent |
| Total | 99.90 per cent |
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The compounds were fired to about 1200°C. Another analysis, made by Hamid of a fragment of a small jar, light blue in colour and made of this vitreous paste is as follows:
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| | Per cent |
| Silica | 85.90 |
| Ferric oxide and alumina | 6.74 |
| Lime | 1.73 |
| Magnesia | 0.38 |
| Alkalies | 3.70 |
| Oxide of copper | 0.46 |
| Loss on ignition | 1.49 |
| Total | 100.40 |
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Marshall thinks that this vitreous paste was an Indian invention and it very slowly spread from that country. It is a distinct advance on faience, though he doubted whether its colour was always as fine as it has little or no surface glaze. (MS-II, 574-76, 582; MCK, 496)