I. M. Godfrey and D. Gilroy
The camera obscura described by Leonardo da Vinci in his notebooks had been used by artists for centuries as an aid to sketching landscapes. The effects of light on silver salts had also been known for some time. In the 1820s Frenchman Joseph Niépce produced images which he called heliographs using bitumen on a pewter plate. The first photograph, taken in 1826, needed an eight-hour exposure. It was not until the mid-1830s however, that the French scenic painter Louis Daguerre discovered a practical method of producing a photograph.
In the early 1830s Thomas Wedgewood experimented with making images using silver salts on paper and in 1835 Daguerre achieved a major breakthrough. By accident (a broken thermometer) he discovered that mercury fumes were able to develop a latent image on an exposed silver plate that had been sensitised with iodine. By 1837 he had developed a working process and in 1839 he formally announced his discovery. The images produced by this process became known as daguerreotypes (Figure 1).
Daguerre’s work prompted Fox Talbot, an English gentleman scientist, to present papers on his own discoveries. In 1835, at the same time as Daguerre, he had produced negative images on silver sensitised paper which he called calotypes. On hearing of Daguerre’s discovery he sought to improve on his imperfect images. Eventually, in 1840 he was able to produce a paper negative from which a positive paper print could be made. These he called photogenic drawings. Also at this time another Frenchman, Hippolyte Bayard, was experimenting with sensitised paper prints, exhibiting them on June 24 1839, before either Daguerre’s or Talbot’s methods were announced.
The French Government offered Daguerre a lifetime pension if he would reveal the details of his discovery. This he did in August 1839. The process was offered free of charge throughout the world, except in England where patents were enforced.
The daguerreotype was far superior to the calotype in detail and was far more popular. The advantage of the calotype, allowing a number of copies to be made from one negative, was outweighed by the fact that it could not match the quality of the daguerreotype.
The major drawbacks of Daguerre’s method were the cost and its inability to produce multiple copies. The product was a direct positive, being exposed in the camera and then developed to produce a one-off positive image. If a second copy was required then a second sitting had to be arranged and the same price paid.
In 1851 the English sculptor and photographer Frederick Scott Archer started using collodion, a mixture of gun cotton (cellulose nitrate) and ether on glass photographic plates. A negative image could be produced if a glass plate was coated with collodion and sensitised with silver nitrate and potassium iodide, exposed and then developed while still wet or tacky. The resultant image was of greater sensitivity than either the daguerreotype or the calotype. When this image was backed with a black card a positive image was produced. This new photographic method was called the ambrotype and it rapidly superseded the daguerreotype and the calotype.
A cheaper offshoot of the collodion process was the tintype or ferrotype. Despite its name it was iron and not tin that was used in this process. A sheet of iron was coated with tacky collodion and exposed in the camera while still wet. It was then developed, fixed, dried and varnished. Popular from the late 1850s, it was used by travelling photographers until the 1940s.
It was the wet plate negative however, that dominated photography till the 1880s. When contact printed onto albumen paper and toned the result was a lovely warm, purple-brown image.
The development of the gelatin dry plate in 1880 and its use on paper signalled the end for the wet plate and albumen process. The gelatin negative and positive system became the basis of modern photography.
Photographic applications have become as diverse as its practitioners. There are photo-ceramics, photo-jewellery, cloth prints and prints on glass, leather, metal and ivory. There are also photo-mechanical processes, pigment prints and numerous colour processes. Despite the proliferation of photographic formats, this chapter focuses on those formats that are most commonly found in major collections and those in smaller institutions and private hands. The main photographic types normally found in collections are outlined in the section below.