Calotype

Calotype or talbotype is an early photographic process introduced in 1841 by William Henry Fox Talbot,[1] using paper[2] coated with silver iodide. The term calotype comes from the Greek καλός for 'beautiful', and τύπος for 'impression'.

Contents

How calotypes work

The sensitive element of a calotype is silver iodide. With exposure to light, silver iodide decomposes to silver leaving iodine as a free element. Excess silver iodide is washed away after oxidizing the pure silver with an application of gallo-nitrate (a solution of silver nitrate, acetic, and gallic acids). As silver oxide is black, the resulting image is visible. Potassium bromide then is used to stabilize the silver oxide.

In the case of salted paper, the sensitive element is silver chloride formed when the salt (sodium chloride) reacts with silver nitrate.[3] Silver chloride decomposes when in contact with light forming silver and chlorine evaporates. Excess silver chloride is washed out of the paper and the silver oxidizes in contact with gallo-nitrate. The silver oxide is stabilized on the paper with hyposulphite of soda.

Silver chloride is sometimes favored over silver iodide because it is less sensitive to temperature. During long exposures in direct sunlight the temperature on the paper can be quite high.

The calotype created a negative image on the silver iodide from which positives could be printed (onto silver chloride paper). This made the calotype superior in one aspect to the daguerreotype which only made one positive image (whereby it was difficult to get multiple copies).

Use and popularity

Daguerreotypes were much more popular than Calotypes.[4] When Calotypes were introduced Jan. 31, 1839,[5] Talbot patented the idea in every country.[6] Because of this, everyone who used Calotypes had to pay royalties.[7][8][9] On the other hand, daguerreotypes were patented only in England, so in America and other places, it could be used freely.[10] Few calotypes were made in the USA.[11]

Another main reason for calotypes being less popular was that paper was used for the negative.[12] Because calotypes used opaque paper instead of glass or film for the negative, when prints were made from the negative, the fibers in the paper would cause the positive print to be fuzzy, as compared to daguerreotypes, which were usually sharp and clear[13][14]

References

  1. ^ http://www.loc.gov/pictures/collection/dag/timeline.html
  2. ^ https://www.ncjrs.gov/pdffiles1/nij/225328.pdf
  3. ^ http://www.loc.gov/teachers/classroommaterials/lessons/world/studentprep.html
  4. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  5. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  6. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  7. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  8. ^ http://wcc.wilkescc.edu/barkerb/GRA140/notes/History_of_Photography-Notes.pdf
  9. ^ http://www.rleggat.com/photohistory/history/calotype.htm
  10. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  11. ^ http://www.loc.gov/rr/print/coll/589_calotype.html
  12. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  13. ^ Carlebach, Michael L. (1992). The Orgins of Photojournalism in America. Smithsonian Institution Press. ISBN 1-56098-159-8. 
  14. ^ http://www.loc.gov/rr/print/coll/589_calotype.html

External links