Tile work at the gates of Mughal Sarai, Doraha, are quite unique in their make. They seem to be made with a technique that was popularly known as Kashi work.
Kashi work consists of a layer of glass spread on a hard kind of plaster; sometimes on a material porcelaneous in structure. The glass was found to be an ordinary silicate colored by metallic oxides and the plaster composed of a mixture of lime and siliceous sand, the hardness being due to silication, which accounted for its bearing the heat required to fuse glass.
If we look closely into the area where tiles seem to be lost (Picture 2 and Picture 3), we find that there are just a few tiles that are lost completely. In most of the area only the glassy coloured surface (glaze) is lost.
Let us see closer into the
structure/anatomy of the tiles used here on this site. We find that the tile work consists of three parts: 1st, the plaster is called khamir(body); 2nd the glass called kanch (glaze); and 3rd, a material called asthar (slip) put between them.
At this site, we find that most have the tiles have lost their surface layer that is glassy and coloured. Some such areas can be confirmed in picture 5, where red arrows (without yellow outline) show the tiles where a little amount of glassy surface layer is still left.
If we closely look at the Tiled surface of the gate, we’ll find that we should not take out the thick body of the tiles (khamir) that is still there, to replace with new tiles. They are quite compact and strongly fitted in the mosaic pattern. To remove the body of the tile is neither feasible nor ethically advised.
Glaze composition and technique
The glazes are made of plant ash alkali flux with colourant (lead-tin /cobalt / copper). Cobalt oxide, used in the colouring of the dark blue glazes. Other pigments found employed are lead–tin yellow, in the yellow and green glazes, and copper oxide, in the turquoise and green glazes.
First operation in making of glaze is to make an easily fusible glass by melting powdered siliceous sandstone with carbonate of soda. Portions of the glass are pounded, mixed and fused with metallic oxides to produce glasses of various colors. The colored glasses are then pounded, suspended in a viscid fluid, made from mucilaginous plants, and painted over the asthar, and the whole is placed in the furnace till all the glass on the surface is fused.
Since more than 97% of the tiled area has compactly-fixed and secured tile body (most of the thickness of tile- 1.5 – 1.7 cm) in the mosaic pattern, it is advisable not to disturb them and do whatever agreed upon treatment ‘in situ’ on the surface.
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