Minerals and Metals in Ancient India v1.c11.s10: Clay

Minerals and Metals in Ancient India v1.c11.s10

Language: English

v1.c11.s10.t1 Glazed Pottery — 11 parts

Clay

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It is a known fact that brick, pottery and miscellaneous terracotta objects have been found in abundance at the Indus Valley sites, specially at Mohenjo-Daro. Now most of the pottery was made of clay of a good quality. Both Marshall and Mackay are of the opinion that the inhabitants used the local alluvial clay for their making of the potteries. This clay is slightly different from that used by the potters who practise their art in the vicinity at the present-day. This alluvial clay requires comparatively little tempering material and burns a pink or light red colour. (MS-I, 289, MS-II, 686) The clay sometimes became rather porous and even fissured on being baked owing perhaps to insufficient kneading, but it answered the purpose extremely well and very creditable specimens of potters’ art were made with it.

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Sometimes a clay was employed that burned grey. Its use was limited, which proves that object of this ware were not importations, but the clay itself may have been imported. Clay of this kind apparently required no tempering and only in exceptional cases was some other substance mixed with it for this purpose.

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Another grey ware was also used in the ancient time. Only a small quantity of it has been found from Mohenjo-Daro. A remarkable feature of this ware is the soapy, unctuous feeling that it provides on touch.

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A third kind of clay used at Mohenjo-Daro produced a ware of a very light pink colour and exceptionally compact in texture. It was occasionally used. This kind of clay was never tempered with any other material. (MCK, 174-75)

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The degraissants used were mica, sand and lime, alone or more rarely in combination. Marshall thinks that there seems to have been a natural admixture of sand in the alluvial clay used at Mohenjo-Daro. Mica is very common and betrays itself by its sparkle. This substance is very frequently found in the sand on the banks of the Indus and is readily extracted from it by levigation. It is especially useful as a tempering material in that when properly mixed with the clay, it greatly adds to the case of working the latter on the wheel; it also facilitates the drying of the pottery without cracking. Lime is commonly present in the fabric of both small and large jars which works as a tempering material confined only to Mohenjo-Daro material. The particular use served by lime as a degraissant still remains a matter of opinion, but with certain clays it appears to be an indispensable ingredient, and it has been mixed with them from the earliest time. (MCK, 176; MS-I, 289)

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The prevailing colours of the potteries are red of salmon, and these are due to the presence of iron compounds in the clay. The pottery is sometimes covered with a slip of bright red colour due to ferric oxide or painted with designs in black or chocolate which owe their colour to manganese oxide. The red slip is prepared by levigating red ochre or *multānī miṭṭī* (a yellow ochreous earth) with water and employs a maganiferous haematite for the black or chocolate shades. The manganese ores which are frequently associated with ferric oxide impart a pure black colour when rich in manganese, but chocolate when the proportion of iron preponderates.

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A noteworthy variety belonging to this group is represented by a number of fine earthenware bangles, usually black in colour, sometimes mottled white, but all distinguished by their fine vitreous texture. The chemical analysis shows a composition of large proportions of lime and magnesia. Their black colour is due to ferrous oxide which indicates that the firing took place in a reducing atmosphere. On the other hand, under the oxidizing conditions prevailing in the kiln, the lime and magnesia would bleach the colour due to iron and the product would emerge white instead. The different colours of the bangles can thus be identified. (MS-II, 686)

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The pigments found on polychrome and painted pottery are black, white, red, yellow and green. The black is carbon, the white implies gypsum and lime. The red and yellow are the well-known ochres. The green is free from copper, owing its colour to an iron silicate indicating terre verte. Lumps of ‘green earth’ (glauconite) which occurs in cavities in the Deccan Trap have been found at Mohenjo-Daro and it is very probable that this material was employed as pigment, after necessary purification.

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Chemical analysis of some ceramic materials and mortars found in Mohenjo-Daro are presented in Table 3.3.

Glazed Pottery

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Several glazed potteries have been noticed at Mohenjo-Daro, bearing a design in a series or parallel waves of a milky hue which have the appearance of being on a deep purplish-black ground. The surface is extremely thin, and to a certain extent contaminated with sand and mica. After microscopically examining the pottery it has been suggested that after modelling, the pot was coated with a colouring clay, which was burnished into the surface with an instrument. The surface, was then dipped or painted with a slip, which may have been made from powdered slag, and sun-dried. The pattern was obtained by removing the slip in a regular fashion, with the aid of a comb-like instrument, and the pot was then fired. From the appearance of the body, which is hard and white and contain traces of translucent material, it would seem that the firing has been conducted at a fairly high temperature. (MS-II, 692-93).

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Another most unusual type of pottery has been noticed in Mohenjo-Daro, which is termed as Knobbed ware. It is rarely found and unusual in its technique. The pottery looks light yellow, sandy looking paste, coated with a light-grey slip evidently intended to stimulate faience. The knobs were put on

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Table 3.3(a)

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Chemical Analysis of Ceramic Materials Found at Mohenjo-Daro

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| S.N. | Specimen | Silica | Alumina | Ferric oxide | Ferrous oxide | Manganese oxide | Lime | Magnesia | Alkalies | Copper oxide | Water | Analyst |
| 1. | Black bangle | 54.28 | 19.63 | — | 8.70 | 0.13 | 9.63 | 4.39 | 3.43 | — | — | Mohd. Sana Ullah |
| 2. | Greenish pottery | 52.39 | 17.03 | 5.30 | 2.29 | — | 15.78 | 4.45 | 1.71 | — | 1.05 | do |
| 3. | Faience vase (bluish-green) | 89.76 | 3.86 | 0.93 | — | — | 0.88 | tr. | 4.07 | 0.50 | — | do |
| 4. | Faience bangle (bluish-green) | 88.12 | 3.02 | 1.82 | — | — | 1.26 | — | Na₂O,4.50 K₂O, 0.65 | 0.46 | — | do |
| 5. | Faience tubular bead (chocolate) | 91.07 | 2.44 | 1.15 | — | tr. | 1.28 | tr. | 2.08 | Cu₂O,1.98 | — | do |
| 6. | Steatite Disc. | 57.99 | — | 4.85 | — | — | 4.31 | 27.20 | 3.54 | 1.09 | 2.01 | Dr. M.A. Hamid |
| 7. | Faience Statuette | 57.23 | — | 3.69 | — | — | 6.39 | 28.99 | 1.88 | 0.46 | 1.36 | do |
| 8. | Slip from steatite seal | 61.02 | — | 2.4 | — | — | — | 34.6 | — | — | 1.8 | Mohd. Sana Ullah |
| 9. | Steatite flat beads | 63.65 | — | — | — | — | — | 33.80 | — | — | 1.09 | do |

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Table 3.3 (b) Chemical Analysis of Mortars Found at Mohenjo-Daro

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| Locality | Gypsum | Carbonate of lime | Sand | Alkaline salts | Moisture | Analyst |
| Wall (HR Site) | 74.12 | 2.50 | 20.41 | 1.18 | 1.79 | Mohd. Sana Ullah |
| do | 63.25 | 0.66 | 31.61 | 3.47 | 1.01 | do |
| Tank (SD Site) | 43.75 | 13.78 | 38.04 | 2.47 | 1.96 | do |
| Drain (DM Site) | 56.73 | 24.87 | 16.64 | — | 1.76 | do |
| Vat (HR Site) | nil | 69.58 | 21.71 | 5.44 | 3.27 | Dr. M.A. Hamid |
| Drain and Cesspit (DK Site) | nil | 39.96 | 46.74 | 0.74 | 3.74 | Mohd. Sana Ullah |
| | | Magnesium Carbonate 8.82 | | | | |

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very carefully, one by one and the vase seems to have been subsequently immersed in the slip. The knobs are made of the same material as the vase itself. Later only this type of pottery has been noticed in Europe on Roman times around second century AD.

Linked texts (1)

Mohenjo-daro