"Stereotypes" and "Cliches" as Printing Terms: Addendum to Williams and Abbott on post-1800 power press bibliography:

        On page 29, 33, 66, Williams and Abbott refer briefly to "stereotype plates" as a nineteenth-century innovation, but they never illustrate what a sterotype looks like or explain at length why they were so important to the industrialized production of books in press runs that might total ten or even a hundred thousand copies.  (Early hand-press book press runs might have been as low as 300 to 500 copies, though estimates of Gutenberg's 42-line Bible's press run usually run into the thousands--he knew he could sell that many.)  Perhaps W&A were unconsciously biased against stereotype printing because it, and the introduction of wove paper, obliterated much of the forensic evidence bibliographers had relied upon when analyzing books printed between 1454/5 and 1800.

        The stereotype plate was produced by taking a mold of the original type while it was still imposed on the press.  That type was then broken down and redistributed in the type cases, and the mold was used to produce one or more copies of the entire multi-page type layout.  The third and forth images from the bottom of this Web page show you a sample mold and stereotype plate:  https://printinghistory.org/chesapeake-chapter-140419/

        The plate was made with a rounded shape rather than flat, like hand-press type, because it was bolted to a printing cylinder designed to transfer ink rapidly to individual sheets as they sped by beneath it, conveyed by mechanical "grippers."  The plates would still bear binding signatures as they were set for the original flat-bed press run, and they also would bear any variants from the way the original type had been set.  Stereotypes could not be corrected by "stopping the presses" because the type was a single mass of metal.  In effect, all stereotype print run books look identical to all other print runs using the same types, even if printed years or decades apart.  Hey, what do you expect?  They're just stereotypes!  Thanks to the pioneering research of Elizabeth Haven Hawley, however, we can use microscopic examination of the page edges to detect unique tell-tale indentations made by individual presses "grippers" to distinguish edition copies from each other.  See the wonderfully titled American Publishers of Indecent Books: 1840-1890, Hawley's (2005) doctoral dissertation:  http://www.academia.edu/3303984/American_Publishers_of_Indecent_Books_1840-1890