The drawing under study is made in 1868 (as evident from the signature) and the watermark mentions the paper manufacturing year to be 1866.
‘Watermarks’ are markings put into paper during its production, by making thinner or thicker layer of pulp when it is still wet. It becomes visible when paper seen with light source at the back of the paper.
This drawing was created at Engineering college of Roorkee.The British who were then ruling India had completely banned the use of hand-made paper in all government offices and started the import of machine-made paper from Britain. A few paper mills were later established in India by the end of the 19th century. The paper seems to have a bluish tinge and horizontal, possible wire marks.
Paper made from discolored rags often turned out too yellowish for fine use. Paper manufacturers therefore developed methods of lightly tinting white papers with blue pigments and dyes to visually neutralize their yellowish tonality. This method of “blueing paper” is said to have originated in Holland and was widely practiced in the 18th and 19th centuries. Due to their discoloration over a longer period of time, some of the papers, however, only retain a very faint bluish/greenish appearance.
Conservation consideration specifically for blue paper:
Generally, all blue papers have to be considered very susceptible to light fading and should be protected as much as possible from light exposure.