For centuries scientists have been experimenting with the reaction of light to several metallic salts. In 1802 for instance, Thomas Wedgewood experimented with paper soaked in silver nitrate. The images however, were not permanent, they turned black in light. The year 1839 is generally considered as a milestone in the development of photography. What greatly contributed to the success of the daguerreotypes was that the French government purchased the rights to Daguerre's process and gave it to the world for free.
Daguerreotypes are positive images on copper plates with a highly polished silver surface.
They are delicate and moreover they are unique and cannot be reproduced. The improvement of the process, especially the reduction of exposure time to less the one minute, led to the opening of many portrait studios in all the major cities of Europe and North America. Travelling daguerreotypists set up their equipment in inns or local shops recording their journeys, events, objects and people on a massive scale. The pictures were mostly kept in a protective case, often padded with velvet or silk. Daguerreotypes stayed popular until the 1850s, when they were gradually displaced by photographs on paper.