Well... here goes. From the "Encyclopedia of Photography", p 1738:Originally Posted by Jorge Oliveira
"Then in 1851, an English sculptor, Frederick Scott Archer (1813-1857), discovered that collodian, a viscous solution of gum cotton in alcohol and ether, when spread upon a glass plate, dried to form a thin tough skin. Archer mixed iodide with the collodian and poured it over a glass plate. He plunged the coated plate while it was still tacky into a solution of silver nitrate. The plate was put into the camera before it had dried, was exposed, and developed at once (no indication of what the developer was - I would imagine it involved subjecting the wet pale to fumes of mercury heated to 167 deg. F, and fixing with sodium thiosulfate). The new technique soon replaced both the daguerreotype and the calotype, and until 1880 was the universal way of making negatives."
Continuing, from page 1740:
"A rather specialized use of the wet plate was for making direct positives, called in America "ambrotypes". A negative was laid aganst a black background and made to appear positive. This was a quick way of delivering finished portraits, for sitters did not have to wait until prints were made. They resembled daguerreotypes and were often confused with them. Exactly the same technique was used to make "tintypes" or as they were first called, "ferrotypes," except that thin sheets of iron jappaned black were used instead of glass."
Interesting. The wet plate had to remain wet through the entire process, thus the travelling camera-darkroom (a tent on a tripod) was necessary for wet plate photography outdoors.