The daguerreotype is a unique image made directly on a sheet of copper, plated with silver, and then polished and exposed to iodine vapor, so that it is sensitive to light. The sensitized plate is placed in a camera obscura, exposed, and then developed with mercury vapor, which creates a chemical reaction with the iodine and silver. Mercury deposits form on the plate, the most remaining where the plate received the most light, and the least (or none at all) in the shadows. Then the plate is washed with a solution that removes the rest of the light-sensitive material, so that only the image remains. Finally, it is cleaned with water, dried, and mounted under glass. The process was developed by French artist Louis-Jacques-Mandé Daguerre and scientist Nicéphore Niepce, and was announced to the public in Paris in January 1839.

1. Thomas Cole/ Mathew Brady Studio

2. Mathew Brady with Juliette Handy Brady and Mrs Haggerty/ Mathew Brady Studio

3. Charles Loring Elliott/ Mathew Brady Studio

Past Exhibitions | National Portrait Gallery Home