An Encyclopaedia of Indian Archaeology v1.c16.s16.19

v1.c16.s16.19

For a comparative study of technology (1) a glazed sherd, (2) an ordinary black-painted sherd, (3) a graphite-coated sherd, and (4) NBPW sherds from RAJGHAT⁴ were subjected to preliminary testing in the laboratory of the Dept. of Silicate Technology, Banaras Hindu Univ. with the guidance and help of the members of that Dept. The test showed: *hardness*: except (1) all can be scratched with knife; *permeability of water*: except (3) which shows permeability of water after prolonged soaking, the rest were impervious; *kerosene*: no action on any; *hydrofluoric acid*: while (3) is insoluble, (1), (2) and (4) are soluble and in the last the polish comes of in thin flakes; *blast burner flame*: (1) is softened, (2) burns rapidly, (3) gets oxidized with prolonged heating, and (4) burns easily and the black colour changes to dull red grey at 1000° C; and *appearance under magnifying glass*: (1) shows a smooth, glossy and uniform surface, (2) shows a smooth, glossy but not very even surface, (3) shows dull and shining black patches with not a very uniform surface, and (4) exhibits black colour with a metallic sheen with a more uniform surface than (3) but not so smooth as (1). The effect of heat on the NBPW sherds shows that the polish does contain some fusible material like borax. In some of the fired pieces the surface shows some slight colour indicating the presence of some colouring metallic oxide like copper or iron added in a very small proportion. In some sherds the surface shows bloating of the body indicating that some very fusible flux got into it as an impurity; on the subsequent firing it fused into slag resulting in bloating of the pieces.