Here is a Conway Stewart green marble fountain pen with a 14K nib; the Duro was made 1920-1940.  Along the side of the pen is: "Conway Stewart, Executive 60". On the nib, it says: "Duro, Conway Stewart, 14 CT Gold".  It is in very good condition but we have not tried to use it.  The company logo is on the fill lever and the clip of the pen.  There are no bite marks, the pen is about 5 inches long.  This pen is from the estate of a lovely English gentleman who used the pen into the 70's.