In the 1930's and 40's this peculiar postcard style was very common in the US. The pictures are BW photographs that are color tinted, and printed on a textured paper. The resulting image has a mostly, but not entirely photographic look. The reason for their being is technical: The advancement of printing technology allowed printing on high rag content paper that was also cheaper. Hence the textured feel. Color photography already existed at the time but the technology for its easy and cheap mass reproduction didn't become available till the early 50's. I picked up a stack of these cards in an antique mall in Indiana. I got more in L.A. later. I'm pretty sure this set of four is from Indiana however. What made them especially interesting for me is the commentary meticulously typed on the back. It doesn't seem like they were ever mailed, but rather that were kept as a sort of travel diary.
Instead of scanning and post the back of each card I decided to enclose the commentary in type.
"This shows how California irrigates. They are fined if water is allowed to overflow the ditches and waste."
"This shows some of the many kinds of dessert plants. We saw many, but not all of these - the prickly pear, Joshua tree, yucca, Spanish bayonet, the ocotillo etc."
"Looking in from the Pacific Ocean across the Golden Gate bridge in the foreground, with San Francisco pininsula (sic) at the right and center of the card and the San Francisco-Oakland bridge in the distance."
Personally I find these cards much more visually appealing than the "Photochrome" cards that replaced them in the 1950's. Interestingly I haven't yet seen similar cards from Europe - though I'm hardly a postcard expert.
1 day ago