The vast majority of real-photo postcards were created in black and white, although some images were hand colored after printing. As camera technology improved and manufacturers moved toward a standard 35mm negative size, printing methods were adapted so postcards could continue to be developed from photographs. For example, the introduction of Kodak’s Velox rapid projection printer in 1937 meant that real-photo postcards could be easily mass produced through enlarging. Imprecise enlargement methods used during the '30s and '40s often required the addition of a decorative white border, which became customary on later photo cards.
Since it was expensive to have additional descriptive information printed on the reverse side of each postcard, many RPPCs made by smaller studios have no text to identify their images. Alternatives to printed text included using a company's handstamp or embossed mark, or exposing text directly onto the photograph’s negative.
The introduction of the CMYK color printing process in 1934 destroyed the popularity of real-photo postcards; though printed using lithography techniques, the resulting photochrome cards resembled color photographs. In 1939, Union Oil became one of the first companies to give out free photochrome cards at its service stations, and the style quickly caught on. Large corporations took over most postcard production, since the photochrome printing methods were easily mass produced and required no retouching, as many real-photo images did.
While photochrome cards featuring images printed on glossy paper are often mistaken for real-photo cards, the two can typically be distinguished by looking under a magnifying glass. Real-photo postcards are recognizable by their smooth gradation of color and form, whereas photochrome printing techniques created shapes from miniscule dot patterns.
All genres of RPPCs are collectible, though some particularly popular subjects include follies or pinups; sports teams; important historical events or expositions; ocean liners, airplanes, or zeppelins; images of soldiers or wartime; and portraits of children. Photographic postcards showing individual people are most desirable if they display specific occupations, mechanical equipment, uniforms, or toys.


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