David Octavious Hill and Robert Adamson, Greyfriars' Churchyard
c. 1845
David Octavious Hill was a painter who was commissioned to paint a large-scale picture, which was to include several hundred portraits, commemorating the founding of the Free Church of Scotland. Instead of having each person sit for a portrait, which would be incredibly time-consuming, Hill decided to photograph each person and then paint the portrait from the photo. Enlisting the help of David Hill, a chemist, they decided to use Talbot's calotype process because it was less expensive and more portable than the Daguerreotype. Additionally, because the prints lacked detail, it allowed Hill more freedom as painter. In addition to these portraits, Hill and Adamson photographed landscapes and locals as well. Since they were working so much with the calotype, they helped to refine Talbot's process.
Eventually, Talbot's negative/positive process becomes the dominant photographic process because it was less expensive and more portable than the Daguerreotype, but more importantly, it allowed for multiple copies of an image to be made from a single negative. The process we use today is a direct descendent of Talbot's calotype.
From paper to glass
Francis Frith, The Sphynx and the Great Pyramid, Geezeh
c. 1857
One of the problems with the calotype process was the use of paper as a substrate. Regardless of how thin the paper is, there is always texture to it; wax was often applied to paper to make more transparent. Eventually, paper was replaced by glass, but the smoothness of the glass posed a problem because nothing would adhere to it. In 1851, Frederick Scott Archer developed the collodian process which solved this problem. A glass plate was coated with collodian, also known as gun cotton, a mixture of cellulose, ether, and alcohol. The plate was then sensitized in a silver nitrate bath, placed in the camera, the picture taken, and the plate developed. This process is also called wet-plate photography because it has to be done while the plate is wet. When collodian dries, it becomes impermeable (it was used to treat wounds, almost like a liquid bandage). Interestingly, collodian plates could be used as a negative or a positive, if backed by black material (known as an ambrotype). Blackened tin was also used instead of glass to create a tintype, somewhat of an inexpensive Daguerreotype. Collodian plates used as negatives were often printed on albumen paper, which used egg whites as a binder to hold the silver nitrate.
Let's not forget Hippolyte Bayard
Hippolyte Bayard, Self Portrait as a Drowned Man
1840
It's important to remember that Niepce, Daguerre, and Talbot were not the only people experimenting with fixing an image, one of whom was Hippolyte Bayard. A civil servant in France, Bayard experimented with photographic processes as a hobby and eventually created his own process. He was to announce his discovery at about the same time Daguerre was preparing to announce his, but a friend of Daguerre's persuaded Bayard to wait. When Bayard saw how popular the Daguerreotype was, he felt like he had been cheated and that his process would have been the rival of Daguerre's (it wouldn't have because it had the worst aspects of Daguerre's and Talbot's as a direct positive on paper resulting in a murky image that could not be reproduced). Feeling as though he had committed artistic suicide, Bayard created Self Portrait as a Drowned Man, one of the first examples of conceptual photography, where the idea (or concept) behind the image is overrides the image as document.
On the back of Self Portrait as a Drowned Man, Bayard wrote:
The corpse which you see here is that of M. Bayard, inventor of the process that has just been shown to you. As far as I know this indefatigable experimenter has been occupied for about three years with his discovery. The Government, which has been only too generous to Monsieur Daguerre, has said it can do nothing for Monsieur Bayard, and the poor wretch has drowned himself. Oh the vagaries of human life...!