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Anna Atkins William Henry Fox Talbot writing on the permanence of the cyanotype process of Sir J. Herschel:
Moreover, we know that some photographic processes are permanent; for instance, the cyanotype of Sir J. Herschel, by which process a lady, some years ago, photographed the entire series of British sea-weeds, and most kindly and liberally distributed the copies to persons interested in botany and photography. The whole of these prints remain unaltered after the lapse of several years.
H. Fox Talbot, "On Photography without the use of Silver", The British Journal of Photography, v. 11, 9 December 1864, pp. 494-495.