Defining the Calotype.

The word Calotype receives much misuse , a quick search with the word on eBay,  reveals cabinet cards , salt prints , Albumen prints , ambrotypes , Daguerreotypes and even sepia silver gelatine photographs described as Calotypes . Clearly this is wrong .

So what is a Calotype ?

The Calotype was discovered by William Henry Fox Talbot on 20th September 1840 and was Patented in England Wales and Berwick on Tweed on the 8th February  1841. Talbot actually thought of the word in January 1840 and it means Beautiful impression. It’s first use in public was 3 days before it was Patented on the 5th February 1840.

The word Talbotype was frequently used in reference to its inventor and to define it from Louis Daguerre’s Daguerreotype  . In Scotland the phrase Edinburgh Daguerreotypes was sometimes used to describe the Calotype and for many years in St Andrews the nursery of modern photography the word  Calotype was used to describe all photography perhaps  out of respect to its inventor by the many early pioneers of photography who practised there but also for the want of a better name .   This dropped out of use once the practise of photography became industrialized in the late 1850s and 1860s and the impressions less beautiful , less artistic but more certain and more scientific.
It must be remembered that at its birth the word Photography didn't exist . The name photography came from the Englishman Sir John Herschel. Meaning Writing with light.

The Daguerreotype is a one off image that is simultaneously both a positive and negative image on highly polished silver plate that cannot be replicated . There is no doubting their jewel like beauty .

Of equal beauty the Calotype is a negative image on fine writing paper  , the transparency of which meant it could be duplicated many times .
The positive up until the early  1850s was by in large made using Talbots earlier invention – the salt print a simple combination of common salt and Silver Nitrate to make silver chloride  ,  in the 1850s Albumen prints became ever more popular . The Albumen print was the invention of the Frenchman Louis Desire Blanquart Evrard who published his process in 1847 . As the name suggests egg whites were used to make a glossy surface on the salted printing paper so that the picture sat on the paper revealing more detail and not inside the paper as with the Salt print. Both the salt print and Albumen print were printed out in good light . Later improvements led to positive papers which could be developed out allowing for mass production in minimal light.  Note this is a positive printing process and not a negative.

Chemically the Calotype uses Silver Nitrate and Silver Iodide to produce the light sensitive Silver Iodide. In Talbots process this was produced by first coating a fine writing paper with Silver Nitrate , this was allowed to dry , whereupon its was then dipped in Potassium Iodide. This produced both silver iodide and Potassium Nitrate,  the silver iodide penetrates the pores of the paper and is Insoluble.  The Potassium Nitrate must be washed out ,  failure to do so makes for at best an unreliable paper or at worst an unusable paper. The resulting paper was dried and is not light sensitive because the potassium iodide is in excess ie it supresses the Silver Nitrate. This is  known as a double iodide of silver and Potassium.

Once dried it is ready for the next stage , sensitization.  More Silver Nitrate is added to make it exquisitely light sensitive. Or to be accurate a mixture of Silver Nitrate  and Acetic acid called Aceto Nitrate was mixed with Gallic acid to form Gallo Nitrate. The Acetic acid was used to keep the whites of the negative white and was used in relatively large amounts , resulting in long exposures when compared to later photographic processes such as wet plate collodion. This was then mixed with a saturated solution of Gallic acid this is a weak solution often less than 0.4% . Gallic acid is very difficult to dissolve completely in cold water.
The resulting Gallo Nitrate was brushed on to the paper and then blotted  dry or at least just damp.

When Talbot discovered the Calotype process he had been experimenting with double coating his salted papers to make them more sensitive and using Gallic acid in an effort to make it even more light sensitive . In reality the inclusion of Gallic acid simultaneously  develops the picture as it is exposed.
What is meant to happen is that when you take the paper from the camera after exposure is that you have a blank piece of paper with an invisible or latent image . This is then developed out with the same solution of Gallo nitrate as before . This is brushed on and the image is revealed. This must have been like magic to the Victorian imagination and may I say still is !

In reality the inclusion of Gallic acid in the Sensitizer caused many many failures . It is very sensitive to heat and was extremely volatile in the heat of an English summer . Sometimes an exposure can be made and there is a very distinct image on the paper when taken from the camera , other times the paper has turned brown and is useless. Only the Adamson brothers had the wisdom to leave it out of the Sensitizer this producing a more certain method of making a Calotype.

From its announcement in 1840 and at its height in the 1850s the word Calotype always referred to a negative on Paper produced using double iodide of silver and Potassium  The method of production evolved and was simplified and made more certain over the years and some times other chemicals were added to make the paper more sensitive or give a better tonal range. These included common salt , Potassium Bromide and Barium chloride. But the result was still a pre silvered paper with an excess of iodide. Such additions were classified as improvements to the Calotype process.

Later methods of producing negatives on Paper mainly from Europe ,  such as the Waxed paper process , serum process and Albumen paper all involved , first coating the paper with a Iodide mixture always potassium iodide often with potassium bromide and sometimes other iodides such as fluoride and Cyanide. This was could be far simpler and less time consuming to produce than Double Iodide . Although in an 1850s version of the arms race some photographers included as many as ten different ingredients in their iodizer . Most of which were not necessary or beneficial !

This was then sensitized with a strong sensitizing solution of Aceto Nitrate with no Gallic acid in the Sensitizer. Some processes had to be used whilst the paper was wet others permitted the paper to be used dry . In most instances exposure was longer than with Talbots Calotype process. In some process the resulting Potassium Nitrate has be washed out just as before . Usually this washing stage is shorter than with Talbots Calotype . They were all developed with a solution of  Gallic acid often a very strong one which necessitated the water being heated in order to dissolve the Gallic acid .  In the journals of the day these methods of producing  negatives on paper were never called Calotypes. The word Calotype was by in large not used on the continent .

The method of coating the paper usually differed too . in England the chemicals were applied with a brush . With a continental process the paper was floated or immersed in a bath of the relevant chemistry .

 The resulting negatives are all very similar in appearance  and the whole genre was referred to as photography on Paper as opposed to the Collodion process or photography on glass .

The sharpness of glass negative  and in the right hands tonal rendition of this  photography on glass is of course what caused the demise of the Calotype.

So  to summarise the Calotype is a photographic process on fine writing paper , made with  double Iodide of Silver and Potassium in the initial stage to produce a negative which can be duplicated multiple times.
It is not and never has been a positive printing process . The positive prints may be produced from a negative on Paper but this   does not make them Calotypes .


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