Robert A. Siegel has just published their sumptuous auction catalog United States Stamp Treasures: The William H. Gross Collection which can be downloaded as a PDF. Although collectors will focus on the mouth watering items with their thorough documentation, I did want to mention the interesting introduction by Scott A. Trepel titled "The Sixth Wave."
Mr. Trepel divides formation of the greatest stamp collections into six waves. The first wave collections were largely worldwide and put together by the titans of philately, of which Ferrary was arguably the greatest. (I particularly like Trepel's observation that "... these [first wave] collectors had to collect in Ferrary’s world, which limited the availability of many outstanding items"). Many of these collections were dispersed around the First World War in turn making possible the Second wave. Caspary and Burrus are among this group. The Third wave dates from the 1950s and these collections are almost all specialized with Lilly being a notable exception. Trepel's remaining waves are seen through the lens of United States collections, with the sale of the Gross collection making possible a sixth.
For each of these waves, in addition to the collectors, there are also associated legendary dealers and auctioneers who were instrumental in their formation, such as the Weill Brothers. (Included in the catalog are thumbnail photos of some of the most famous collectors from each of these waves.)