Minerals and Metals in Ancient India v1.c11.s8: Seals
Minerals and Metals in Ancient India v1.c11.s8
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Seals
v1.c11.s8.1
Of all the objects those have been unearthed at various levels from Mohenjo-Daro, perhaps the most interesting ones are seals or fragments of seals. On the basis of shape, the seals of Mohenjo-Daro can be conveniently classified under ten different groups. There was a method of manufacture of these seals and Sir John Marshall has tried to highlight this aspect.
v1.c11.s8.2
The stone seals were first cut into shape by a saw, whose thickness was 0.025 inch. After the seal had been cut to the required size, if it was to have a boss, this was roughly cut into shape with the saw, a horizontal cut was made from each side of the seal towards the centre and four vertical cuts were then made downwards to meet the horizontal ones. A rough square projection of the size of the boss was thus left at the back of the seal. The boss was then carefully rounded off after the groove, that always runs across its centre, had been roughly made by a V-shaped cut. The rounding off of the boss was apparently done with a knife and finished off with an abrasive, after which a hole was bored through it from opposite sides to take cord. (MS-II, 377)
v1.c11.s8.3
Almost all the seals are coated or have been coated with a smooth glassy-looking substance which was at first thought to be the remains of a glaze, whose colour has entirely disappeared. All the seals have been carefully examined for traces of colour, but without success. But the same seals of Mohenjo-Daro and Harappa which have been found at Kish in Mesopotamia contain traces of original blue or green colouring. There is no evidence that seals of Mohenjo-Daro were originally coloured. If these were so coloured, all traces of the pigment have entirely disappeared through long deposit in the damp and salty soil of the site. Sana Ullah has made an exhaustive analysis of the surface coating on one of these seals which has given the following results:
v1.c11.s8.4
| 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 |
| Total | 100.00 per cent |
v1.c11.s8.5
In another seal, the amount of water was found to be 2.17 per cent. The analyst remarks that “the surface substance is steatite or talc that has been deprived of the greater part of its water, which is only possible by ignition”.
v1.c11.s8.6
Therefore it seems that the coating upon these seals is made of the same material as the seals themselves. There is reason to think that the coating was an applied one, for it scales off in the same manner as a slip would do. Possibly before a seal was considered ready for engraving, it was coated in order to cancel blemish and was then baked in a kiln. The result of the firing was undoubtedly to whiten and improve the outside surface. (MS-II, 379)
v1.c11.s8.7
Mackay is also of the same opinion when he says that there is no doubt that after being cut and engraved, these seals were treated in some way to produce the white coat that covers them. Horace Beck, after microscopically examining the white coating, has came to the conclusion that it is not a slip, but was made by painting the surface with an alkali and then subjecting it to heat. Sometimes this coat shows a certain amount of lamination caused either by the alkali being applied in more than one coat or by the overlapping of brush marks.
v1.c11.s8.8
Mackay does not think that this coating was invariably applied. If the steatite used for the seal was a good white specimen, then the coating would not have been needed; but when the stone was grey or black or otherwise impure in colour, a white surface was evidently considered essential for aesthetic reasons. Some of the seals are made of a fine black steatite and these still show in many parts that they were carefully coated with white material. Besides whitening the surface of the seal, the baking would materially assist in hardening it owing to the loss of water. (MCK, 346)