Joel Davis, Brian Ingram, age 15, of Santa Rosa, Calif., 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 daguerrotype in 1839.

The first daguerrotype uses a polished, silvered copper plate made light sensitive by subjecting it to idodine fumes. Daguerre then exposed it from three to 30 minutes in a camera. He developed the image of 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, mirrorlike areas which appear dark when the plate is held to reflect a dark field.

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

In the 1800s, Americans used daguerreotypes a great deal, especially for portraits.