History of the format 

Postcards were the emails and iPhones of 1909. Increased postal service allowed people to send a written (text) message along with a photo (image) they had made themselves on a photo postcard. The international trend was at its strongest from about 1905 to 1930, but postcards remained in high use until the 1950s. Although it may seem outdated now, the postcard collecting craze was the result of an era undergoing more disruptive social and technological changes than we are experiencing today. 

Process 

In 1903, the Kodak company released the 3A camera, which allowed people to create their own photo postcards. In conjunction with the 3A developing kit, people could make photo postcards at home with relative ease. Many of these early postcard prints were made in the trendy sepia-tone, a process that leaves the image a warm brown colour rather than the stark black and white look that silver-gelation prints are known for. Cyanotype postcards were also popular with the layperson photographer, prized for their rich blue colour and simple processing technique.    

How the format was used 

New camera and printing technology and relatively cheap equipment allowed entrepreneur photographers to be a part of the postcard explosion. Many of them travelled with carnivals to sell portrait cards or toured their regions to produce view cards to sell in their hometowns. Early postcard cameras used glass plate negatives; however, the introduction of nitrate film reels made the technology much more portable.   

There are two basic types of photo postcard: The view card showed scenes of places including local scenes, main streets, buildings, features, etc. The topical card captured events or subjects like a flood or fire, weddings, parades, outings and portraits.