This page is the starting place for identifying a machine cancellation on mail from the United States in the general period pre-1920.
Some of the information used here came from the Machine Cancel Society and other pointers to particular cancellations were derived from the very fine book Postmarks on Postcards by the late Richard W. Helbock .
I highly recommend Mr. Helbock's book as a great starting-place for new cover and card collectors who want to learn more about postmarks. The book covers only the postcard era (1900-1920) in the United States. I urge you to purchase your own copy of the book. You can purchase it from these sources: Amazon Kindle edition of "Postmarks on Postcards" from Amazon, or copy of "Postmarks on Postcards" from James Lee.
A very good overview of machine cancellations is available from The Machine Cancel Society in the form of an award-winning exhibit on the history of Boston machine cancels, by William Barlow, Jr. (recently updated) Viewing this exhibit is a great education in not only the evolution of machines in a major U. S. city, but also helps the reader to understand that these early cancels can sometimes be difficult to identify.
My web pages are here for one reason: to help you to identify the machine cancel on a cover or card from before 1920.
So, let's get started. Keep the cover or card (or a photocopy) in front of you, and follow the information and links on this web page.
First, a quick nomenclature lesson:
Note that the "cancellation" or "killer" is the part
that prevents the stamp from being reused. The "postmark"
or "dial" is the part of the impression that tells you where the letter
was mailed and when. Various dial designs were based on
in use by U. S. post offices of the 19th century.
However, when machine cancel inventors approached the problem of cancelling the stamp, they used a great variety of designs to ensure that the stamp was obliterated by ink, even when a cover or card was machine-fed at high speed.
If you want, you can jump directly to the webpage with a list of machine cancel dials and killers. You pick your item from the page, based on the design, and will be sent to a page or pages that will guide you in the identification. Alternatively, you may follow the question-and-answer flow that follows:
Page Layout Design Made Possible by:
Updated June 19, 2015
Copyright©1996 - 2015 Robert Swanson