Brian Faulkner, age 15, of Barre Vt., for his question:

WHEN WAS THE FIRST DAGUERREOTYPE MADE?

A daguerreotype is one of the first forms of photographic print. It was named for its inventor, Louis J.M. Daguerre. He made his first daguerreotype 150 years ago, in 1839.

The first daguerreotype used a polished, silvered copper plate made light sensitive by subjecting it to iodine fumes. Daguerre then exposed it from three to 30 minutes in a camera. He developed the image in mercury vapor and "fixed" it with sodium thiosulfate.

Improvements made in 1840 increased the sensitivity of the plate by bromine fuming and enriched the image by toning it with gold chloride.

The highlights of a daguerreotype are whitish. The shadows are bare, mirror like areas that appear dark when the plate is held to reflect a dark field. During the early 1800s, daguerreotypes were especially used a great deal for portraits.

After 1851, a wet collodion process gradually took the place of the daguerreotype.