| Some other ways to date the French vintage postcard: The postmark: When a card is postally used, a readable postmark can give you the expedition date of the postcard, not necessarily the age of the postcard !
The technique of how the postcard is made:
There are all kinds of techniques from the printing process to the photographical technique : phototypy, litographie, nuage technique, oranotypie ... Each type of process can be ascribed to a certain period. The paper: brand, quality, color: There are different kinds of paper used in the photography and (real photo) the printing industry. As well, the colour of the paper can determine the period (green, beige, blue, pink..) The editor: On most postcards the editor is mentioned, and each editor was productive in a certain period. Unfortunately, most of information about the editors had disappeared or been destroyed. Some editors changed there logotypes during their activity. There are hundreds of French editors and a lot more European ones.
The stamp: The value and view of the stamp can determine the age of the card. The design: Each period has its own look, for example the art nouveau cards are from around 1900, the heavy coloured photo postcards are typically from the 1920-1930 period. The sign: When a postcard is signed by an artist, the period that they worked may give us a date for the card. | 
