Silver 2 Sensor : Episode 7 – calotypes

In the last episode we saw how daguerreotype process was famous for more than two decades and then brought down by the invention of the newly developed processes like calotype and tintype. In this episode, we are going to see about henry fox Talbot and his invention of calotype which paved way for the modern day film photography process.

Henry fox Talbot was a British inventor and photographer who lived in the same era as of Louis Daguerre. Both worked tirelessly on their own photographic concepts and both got successful at the same point of time. But it took twenty more years for Talbot to make the whole world follow his calotype process.

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Talbot considered photography as an artistic medium. He studied all the photographic processes discovered before him and made note of all the advantages and disadvantages of each process. After doing a few years of research, Talbot tried to reproduce photographic images on paper coated with silver halide (silver iodide used in most cases). He initially started experimenting in 1835 where he used silver chloride coating on a paper and exposed it to light. The paper will get darkened based on the proportion of light falling on it. But this took really long exposure times (one to two hours).

In 1840, the same year Louis Daguerre announced the success of his daguerreotype process, Talbot came up with an upgraded version of calotype process. In this method, the sheet of paper will be coated with silver iodide (from reaction between silver nitrate and potassium iodide). And before loading it into the camera, a mixture of acetic acid, Gallic acid and silver nitrate is coated on the paper. The exposure time for this method is very less (1-2 mins) when compared to traditional calotype process. After capturing the image, the paper is processed using potassium bromide and sodium thiosulfate solution. This treatment of chemicals fixed the image on the paper and creates a translucent negative image.

This negative image can produce many positives through a method called contact printing. In contact printing, a light sensitive material is pressed along with the negative and light source is applied on the negative. This selectively colors the same area on the light sensitive material (like the negative).

But what made calotype a more popular method than daguerreotype. There is a small story behind this. One week before Louis Daguerre made his process public in France, an agent of Daguerre in UK filed a patent. So after the public release of daguerreotype, UK became the only country in the world which had to pay heavy license fee to daguerreotype process. This reason and the ability of calotype to produce multiple positives made it highly popular in the 1960’s

At the same time, Talbot also sold calotype license to photographers for initial fee £20. He later reduced the fee to £4 and waived it completely for amateur photographers. But professional photographers had to pay a huge fee of £300.

Calotype was also called as Talbotype in the honor of Henry Fox Talbot

You can still view the patent filed by Henry Fox Talbot Here

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