The National Postal Museum’s Travers Papers is a collection of more than 4,000 pages making available to historians and collectors official documents relating to the production of U.S. postage stamps from 1847 to 1910. The NPM and the U.S. Philatelic Classics Society have collaborated to make this valuable collection available online to collectors around the world.
You can also read more about the Travers Papers in this 2-volume book available for borrowing from the APRL:
Thomas J. Alexander, George W. Brett, & W. Wilson Hulme II, comp., & Barbara R. Mueller, ed. United States postal history and postage stamps official records (Washington, D.C.: James E. Lee in cooperation with the Smithsonian National Postal Museum, 2011-): v. [In process 000036086; In process 000036087]