Complex sentence: Contrary to the name, linen postcards were not produced on a linen fabric, but used newer printing processes that used an inexpensive card stock with a high rag content, and then finished with a pattern which resembled linen.
Split into simpler sentences: Contrary to the name, linen postcards are not produced on a linen fabric. Thanks to newer printing processes they were produced on an inexpensive card stock with a high rag content, and then finished with a pattern which resembled linen.