Journal of the Asiatic Society of Bengal Part II Physical Science 1878

Thus the whole of the standard maps of the Topographical Surveys on the scale of 1-inch to the mile and the Cadastral village maps of the Revenue Survey on the scales of 32 inches to the mile for Bengal and 16 inches to the mile for the N.-W. [...] After the due preparation of the original the production of the negative is a point of the utmost importance and may well be considered by itself before proceeding to the consideration of the various processes of photographic printing. [...] When maps are not drawn entirely in pen and ink but have the hills brush shaded and it is desired to reproduce them by the collotype or engrving processes great care and skill are required on the part of the photgrapher to get the ground of the negative dense enough to give a perfectly clean impression in the white parts of the map and at the same time prvent the grain of the paper fro [...] 77 the negative representing the lines of the subject it renders the colloid coating insoluble throughout the thickness of the coloured film so that the lines withstand the solvent action of the warm water which entirely removes the rest of the coloured film from the ground and parts which have not been influenced at all by the light. [...] The rate of printing will consequently be more or less dependent on the senstiveness of the paper the strength of the light at the time of exposure and the state of the weather ; the printing operations can moreover only be carried on during the few hours of daylight.