Minerals and Metals in Ancient India v1.c14.s4: Seals
Minerals and Metals in Ancient India v1.c14.s4
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Seals
v1.c14.s4.1
Indus seals were in use at Lothal from the earliest phase of occupation to the latest in Period A and to a small extent in Period B also. The earliest seal is made of steatite. It is of light grey colour and has been used in the manufacture of most of the seals at Lothal, because the material is soft and can be easily cut, engraved and polished. Quite often the seatite paste was pressed into a mould, dried and then engraved and heated for making seals. Three categories of steatite seals have been distinguished. Category A consists of seals made of soapstone with a white coating of the same material producing a greasy lustre. These show a considerable proportion of magnesia and silica. Category B consists of seals made of steatite paste with a pearly lustre and they crumble in moisture. Seals of soapstone without any greasy coating are included in Category C. Besides steatite, agate, ivory and copper were also used. Terracotta seals are not infrequent. (Rao, 306)
v1.c14.s4.2
The process of preparing seals is fairly clear from the lumps of steatite and partially-cut blocks found at Lothal. A rectangular block of steatite was first sawn to the required size and shape. The second stage was to produce a rough square boss, if the seal was to have one, on the reverse by cutting out with saw the unnecessary portions. The hole for the ring, by which the seal used to be held was bored with the help of bronze drills of the flanged type dipping towards the centre from two sides. The tool used for engraving depended upon the material of the seal. For soft substances like steatite, terracotta and soapstone, engravers of chert, ivory and bone were used. In the case of harder substance such as agate and shell, chisels and engravers of copper and bronze were necessary. (Rao, 307)
v1.c14.s4.3
Horace Beck was of the opinion that the surface of the steatite seals was painted with an alkali and then subjected to heat. A careful examination of the alkaline coat indicates the application of more than one coat of the liquid and even overlapping of brush marks. The chemical analysis has indicated that the covering film is made of the same material as the seal itself and appears to have been applied. After the application of the coating, the seal was baked to produce the white exterior while the core itself remained grey or greenish, and hardness was produced with the escape of water from the core. A closer examination of the seals reveals that engraving was done before the seal was fired. The chemical analysis of the white film covering the surface of the seals shows the following composition:
v1.c14.s4.4
Silica - 61.2 per cent Oxides of aluminium and iron - 2.4 per cent Lime - Nil Magnesia - 34.6 per cent Water (by difference) - 1.8 per cent 100.00
v1.c14.s4.5
The quantity of water varies up to 2.17 per cent in some cases. The surface substance is therefore said to be steatite or talc that has been deprived of the greater part of its water, which is only possible by ignition. (Rao, 309)
v1.c14.s4.6
Thus different types of seals have been distinguished on the basis of shapes, i.e., square, rectangular, cylindrical, plano-convex, circular and miscellaneous. (Rao, 309)