Wedgwood's most significant contributions were his experiments with light-sensitive chemicals, particularly silver nitrate, in an effort to capture images permanently. Working primarily in the late 1790s and early 1800s, he conducted systematic investigations into the effects of light on various materials.
His methodology involved:
- Creating "sun prints" or "photograms": He would soak paper or white leather in a solution of silver nitrate and then place objects (such as leaves, insect wings, or silhouette cut-outs) directly onto the treated surface. Upon exposure to sunlight, the areas not covered by the objects would darken, producing a negative image of the object.
- Attempting camera obscura images: Wedgwood also tried to capture images formed in a camera obscura by projecting them onto his sensitized paper. While he was able to observe faint images, the light sensitivity of his materials was too low, and the exposure times required were impractically long for landscapes or portraits.
A critical limitation of Wedgwood's work was his inability to "fix" the images. Once exposed to light, his prints would continue to darken over time, eventually turning completely black. This meant he could not make his images permanent, a crucial step later achieved by inventors like Nicéphore Niépce and Louis Daguerre.
Wedgwood's experiments were documented and brought to public attention through his collaboration with the chemist Humphry Davy. In 1802, Davy published a paper titled "An Account of a Method of Copying Paintings upon Glass, and Making Profiles, by the Agency of Light upon Nitrate of Silver; Invented by T. Wedgwood, Esq." This publication, which detailed Wedgwood's processes and observations, is considered a landmark in the early history of photography, demonstrating the scientific potential of photochemistry.
Despite the impermanence of his results, Thomas Wedgwood is recognized as a pivotal figure in the development of photography. His systematic experimentation and the documentation of his findings laid essential groundwork for subsequent inventors, establishing the fundamental chemical principles upon which photographic processes would later be built. His work represents one of the earliest clear articulations of the concept of capturing images using light-sensitive materials.