Salted paper print by William Henry Fox Talbot (1800-1877). Talbot invented the calotype proces which he patented in 1841. This negative/positive proces meant that any number of prints could be made from the same shot by transferring the negative image on to special paper. Strictly speaking the term calotype refers only to the negative, however, it has also become a term for the positive produced.
© National Museum of Science & Media / Science & Society Picture Library