Hi O/H found this on the web about the silk cards, look like it was a cottage industry sort of thing.
These cards known generally as WW1 Silk Postcards were first produced in 1914 through 1918 and declined substantially in 1919 onwards until ending around 1923. In 1930 through 1945 a machine made card was produced which was simpler and plainer with less variations. They never regained the popularity of their WW1 predecessors which have been estimated at some 10,000,000 hand made cards.
The WW1 cards were generally hand embroidered on strips of silk mesh with as many as 25 on a strip. They were mostly embroidered by French women in their homes and then sent to the factories for cutting and mounting on postcards.
Most cards do not have postage stamps as they were mailed home in the Military Mail Pouches. Samples of machine duplicated designs can be seen in the above photos. However, I am unable to date them.