1941 Cadillac Fleetwood Advertisement

     In an earlier post about a Cadillac fighter plane illustration I had played with the idea that Wally did a great deal of work for General Motors during World War II because of his experience doing illustrations for Cadillac in the late 1930s and early 1940s.  Here is one of those illustrations.

     While a specific date is no where to be found on this illustration, I would guess it is Cadillac's series 67/75 Fleetwood limousine.  It was introduced in 1941 as one of Cadillac's premiere luxury vehicles.  Here's the wikipedia take on this series.  

     What is also interesting about this illustration is that it is a color proving stock for Fortune Magazine, where it was published.  This scan below is the backside to the above illustration for Cadillac.  

     Someday, when I can find the time, I'd love to know more about what this proving stock really is, and what role did it play for Fortune Magazine.  Furthermore, why did my grandfather have this in his possession?