DAGUERREOTYPE PROCESS

Albert Southworth wrote about the daguerreotype process for the general public to serve the double purpose of instruction and the gratification of curiosity:

Daguerreotypes are made upon a surface of silver, plated on a body of copper, about the thickness of a half-dime. When the plate is polished smooth and clean, it becomes a blackground or black board [by reflection] upon which to make the picture. In a dark room it receives upon its surface by evaporation a compound of Iodine, Bromine and Chlorine, forming an even and perfect [light-sensitive] coating. The first light admitted to the coated plate is the desired image made by the light in the Camera Obscura. The light affects the combined elements composing the surface instantaneously, and in exact proportion to the amount admitted. The plate is then placed over a box containing a moderately heated cup of quicksilver [metallic mercury]. The vapor of the quicksilver passes readily through the compound surface of the plate just in proportion to the light acted upon it, and becomes attached to, or amalgamated with the silver. This forms the lights of the picture, and is the white chalk upon the blackboard. The time of the exposure of the plate to the coating, to the image of light, and to the mercury, can only be learned by actual experiments. After the picture is fully developed, it is immersed in a solution of hyposulphite of soda, which does not affect the mercury or black-ground but removes the compound coating. It is then submitted to a process [in a heated bath of gold-chloride] whereby the whole surface of the plate is coated with a leaf of pure gold, which protects it as a varnish does a painting [the plate is then washed and dried]. To secure Daguerreotypes from injury, they are sealed under glass, with a border between, to prevent the glass from resting upon, or chafing them [and are then placed into cases or frames].

Southworth & Hawes employed only natural daylight descending through a large overhead skylight, moderated by a diffusing curtain. The exposure time for most of their portraits was eight to twelve seconds, which required a stabilizing headrest, skillfully hidden from view. For portraits of children, who were likely to move, artistic shading effects were sacrificed by admitting greater light to the subject, requiring shorter exposures of one to five seconds.