Spirits of Silver

A Short History of  the Origins of Photography and the Salt Print

The 1830's proved to be a momentous decade for photography - one that was to culminate with its "official" birth in 1839 with the January 7th announcement of Louis Jacques Mande Daguerre's"invention" of photography delivered to the Academie des Sciences in Paris by Deguerre's friend, Dominique Francois Arago. Arago's announcement, which omitted the details of Daguerre's invention, spurred Brittian's William Henry Fox Talbot into action and on the 25th of January, with the assistance of physicist Michael Faraday, Talbot exhibited a number of what he called photogenic drawings to members of the Royal Institution.  This was then followed by Talbot's presentation of his salted paper process before the Royal Society on 31 January where his paper entitled Some Account of the Art of Photogenic Drawing, or the process by which natural objects may be made to delineate themselves without the aid of the artists pencil was read.  The paper described Talbot's process in general and even gave some thoughts about its future applications.  In a letter read before the Royal Society on February 21st Talbot supplied the working details of his process. Daguerre did not supply the working details of his process until the 19th of that August.

 
But Daguerre and Talbot were not the only researchers that had contributed to the invention of photography.  Since antiquity the camera obscura - the precursor of the modern day camera - had been used as an aid in drawing and to study perspective. In 1725 Johann Heinrich Schulze accidentally discovered that a piece of chalk dipped in silver nitrate turned black from white when exposed to sunlight while the unexposed side remained white. He created crude photographic impressions which eventually turned all black because photographic "fixer" (sodium thiosulfate) had yet to be discovered. In 1737 the French chemists Jean Hellot even suggested using a solution of silver nitrate to write secrete communiques which would remain invisible until after a lengthly exposure to sunlight.

Thomas Wedgewood was the first person known to use light sensitive materials (silver nitrate) on various surfaces placed in the camera obscura in the 1790's. His initial experiments failed because the low sensitivity of silver nitrate required a much longer exposure than he had realized. Wedgewood was joined in his experiments by Humphry Davy who repeated Wedgewood's experiments using silver chloride which is much more sensitive than silver nitrate and this time they were successful in making photograms by contact printing.

But a method of fixing the image remained elusive and the images, once produced, remained sensitive to light and could be viewed only for brief periods in dim light or the unexposed portions would darken until the image disappeared. Initially both Daguerre and Talbot fixed their images using a strong salt solution.  However salt was not a permanent solution and the unexposed portions of the image would gradually blacken until the image disappeared. It was during a social visit to his friend the English polymath Sir John Herschel that Talbot learned of Herschel's 1819 discovery that sodium thiosulfate had the power to “dissolve” the unexposed silver salts while leaving unchanged the reduced metallic silver formed in the image areas during exposure. Talbot immediately abandoned using potassium iodide as a fix and switched to sodium thiosulfate. Daguerre learned of it through a letter Talbot had sent to French physicists Jean Baptiste Biot dated 1 March 1839 in which he listed the known fixing methods and called thiosulfate the best. Daguerre then immediately abandoned salt as his fixer and took up thiosulfate.

Then in September of 1840 Talbot made a discovery that forever changed the course of photography. Until then the images of Daguerre and Talbot were unique and could not be reproduced without re-photographing them.  The daguerreotype produces a latent image on a copper plate coated with silver on one side which is then "developed out" with fumes of mercury.  Talbot's photograms, on the other hand, were formed fully "printed out" on the salted and sensitized paper placed in the camera and then washed clear of the remaining unreduced silver.  But on that fateful day in September while experimenting with papers that were sensitized in various ways while trying to reduce the in-camera exposure time,Talbot poured a solution of gallic acid and silver nitrate over a piece of previously sensitized paper that had failed to produce an image because the exposure had been too short and then saw the previously invisible latent image that had formed begin to appear. Thus was created the first photographic negative on paper from which multiple prints could be made by contact (or much later with an enlarger) printing.

This process he called Calotype which he patented on 8 February 1841. According to the specifications of the patent, paper was first coated with a solution of silver nitrate which was allowed to dry. Next the paper was dipped for a minute or two in a solution of potassium iodide then rinsed in water and again dried. Talbot could store this “iodized paper” in the dark until needed. To make the iodized paper light sensitive he coated it with a solution of silver nitrate, acetic acid, and a gallic acid solution which he referred to as gallo-nitrate. After coating he allowed 30 seconds for the sensitizer to sink in, then dipped the paper in water, dried it, and placed it in the camera for exposure. The negative thus produced was developed by brushing it with the same gallo-nitrate solution, fixed in a solution of potassium bromide or sodium thiosulfate, washed, and then dried. The calotype negative could then be contact printed with the salted photogenic paper introduced earlier

The salt print is the first paper-based process for producing positive prints and was dominate from photography's birth in the 1830's until the mid-1850's when it was largely replaced with the albumin process – a process that is largely the same as the salt print process except that egg white (albumin), potassium iodide, and salt is coated onto the paper (or glass) and dried before being sensitized to light with silver nitrate. When the salt print process was replaced with the albumen process which, in turn, was replaced with the prevailing silver gelatin process of today, it became a forgotten process waiting to be re-discovered among the forgotten and misplaced jewels of the past.

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About the Images:

The images displayed in this gallery were contact printed using 8x10 inch in-camera negatives by exposing a high-quality handcoated 100% cotton rag paper to the action of sunlight - just like they were in the eighteenth and nineteenth century.  Once the negative is obtained, each print requires several hours to process.  Due to daily flucuations in the amount of sunlight (season, time of day, passing clouds, etc.), relative humidity, and the sheer mechanics of coating, drying, and processing the sensitized paper, each print is necessarily a unique one-of-a-kind print - much like an oil painting. They are shown below mounted, framed, and photographed with an "ancient" (2007) digital point-n-shoot camera and posted to this site with low resolution for security reasons.

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Go to the Salt Print Gallery