Silver and Sunlight: The Science of Early Photography

Jane E. Boyd

News of the miraculous pictures spread rapidly, and several people came forward to announce that they had independently developed similar techniques. Among them was William Henry Fox Talbot, the Englishman who had been frustrated by his lack of drawing ability with the camera lucida. Talbot’s interests included mathematics, chemistry, optics, botany, the classics, and archaeology. Working at his ancestral estate, Talbot had devised a process he called “photogenic drawing” in 1834. He coated drawing paper with a solution of salt and then soaked it in silver nitrate or chloride. Placing lace or botanical specimens against the paper, he exposed it to the sun. The resulting silhouetted images were fixed, at least for a short time, with sea salt and potassium iodide.

The next summer Talbot expanded his experiments to include camera-obscura images. Using tiny cameras with large lenses nicknamed “mouse traps,” he succeeded in capturing miniature, negative images of parts of his house. Talbot had abandoned these researches, thinking to perfect them at a later date, but the news of Daguerre’s invention galvanized him. He sent specimens of his work to the Royal Institution in London, wrote to Arago and other French scientists, and had papers read at the Royal Academy describing his process.

By early February 1839 Talbot was corresponding with a friend, noted astronomer Sir John Herschel, who had just begun his own work with camera-obscura images. Herschel coined the term photography, meaning “writing with light,” for the new process. His other major contribution was an improved fixing method, immediately adopted by both Talbot and Daguerre. In his 1839 research notebook Herschel wrote, “Tried hyposulfite of soda to arrest action of light by washing away all the chloride of silver or other silvering salt. Succeeds perfectly.” That compound is now known as sodium thiosulfate, widely called “hypo,” which was used as a fixing agent for many years. By the fall of 1840 Talbot had devised a successful negative-positive paper process, which he dubbed calotype, from the Greek and Latin words for “beautiful image.”

Meanwhile, back in Paris, Arago used his political and scientific influence to press forward with the purchase of Daguerre and Niépce’s process. A fire in March 1839 destroyed the Diorama, Daguerre’s main source of income, and provided a further justification for a financial reward. On or around 1 August, a bill proposing pensions for Daguerre and Isidore Niépce passed into law. The details of the method, however, remained secret until 19 August, when all was revealed to the overflow crowd at the momentous meeting at the Institut de France.

Light Sensation

Marc-Antoine Gaudin, a partner in an optical instrument-making firm, was present that day. Immediately after the event he bought iodine and mercury at a nearby pharmacist’s shop and made a camera obscura from a cardboard box and a spectacle lens. The next morning he iodized a plate, pointed his makeshift instrument outside, waited for 15 minutes, and then vaporized the mercury with a candle flame. The resulting picture was simply a dark silhouette of buildings with the window’s balustrade in the foreground, but Gaudin was thrilled. “Everyone wanted to copy the view offered by his window,” he later wrote, “and very happy was he who at the first attempt obtained a silhouette of roofs against the sky: he was in ecstasies over the stove-pipes; he did not cease to count the tiles on the roofs and the bricks of the chimneys . . . in a word, the poorest picture caused him unutterable joy.” Even the most mundane scene became magical when captured in detail on the daguerreotype’s silvered plate.