How Were Early Photographs Made?

Many different elements—such as silver, gold, platinum, and iron—have been used to create photographs. Daguerreotypes, salted paper prints, albumen prints, and carbon prints were among the earliest photographic processes.

Daguerreotype
Daguerreotypes are made on sheets of copper that have been plated with silver and sensitized by suspending them over iodine. Rising iodine vapors unite with the silver to produce light-sensitive iodide. After exposure to light in the camera, the plate is developed by placing it over a heated dish of mercury, revealing the image in an amalgam of silver mercury.

Salted Paper
Salted paper prints are made by sensitizing a sheet of paper in a solution of table salt and then coating one side with silver nitrate to form light-sensitive silver chloride. After drying, it is exposed to light while in contact with a negative. The image layer consists of particles of silver embedded in the fibers of the paper.

Albumen
Albumen prints are made by floating thin sheets of paper in a bath of egg white (albumen) containing salt. The paper is dried and sensitized by coating it with a solution of silver nitrate. After drying, it is exposed to light while in contact with a negative. The image layer consists of particles of silver deposited on the paper in an albumen binder.

Carbon
The carbon print process was developed to address the problem of image fading with silver-based photographs. Paper coated with pigmented gelatin is sensitized with potassium bichromate, which hardens during exposure in proportion to the amount of light received through a negative. The soft gelatin is then washed away to produce a final positive image.