Petert4522 is right ---it was a fantastic article in the November 2015 issue of "The United States Specialist".
Anyone who is truly interested in and collects U.S. stamps and postal history should be a member of the United States Stamp Society
Log-on the USSS website now and learn for yourself. Why wait? Act now….
http://www.usstamps.org/They have great study groups that include the: Prexy Issue; Americana Series; Dummy Stamps; First Bureau Issue; Luminescence; & Registered Mail
Additional Stamp Committees include: Booklets & Booklet Panes; Bureau Precancels; Encyclopedia; Essay-Proof; Fourth Bureau Issue;
Liberty Series; Marginal Markings; Modern Postal History; Plate Numbers Check List Service; Durland Editor; Presidential Issue; Revenue Issues;
Second Bureau Issue; Vending & Affixing Machine Perforations; and Washington-Franklin Head Issues.
And their monthly 48-page, full-color publication is top-rate.
You won't go wrong.
Hal