Over the last 20 years there has been a resurgence in the interest of letterpress and printing with metal type. Lead type and old presses sitting in storage or old barns, basements are finding their way back into use in the artist studio and small press shops. There are plenty of new books on the subject, but the technology really hasn't changed over the last 100 years and there are plenty of books out there that are no longer copy righted that can be freely viewed, downloaded and printed.

In addition to the online material, there are several museums dedicated to preserving the rich history of the graphic arts, printing and typesetting technology, and printing craftsmanship. They often offer workshops, libraries and access to hard to find items.

The following is a list of letterpress resources, some I have download, while other are links to documents that can be viewed, or dowloaded.

Printers' Marks: A Chapter in the History of Typography by W. Roberts https://www.gutenberg.org/ebooks/25663
The Art and Craft of Printing, by William Morris https://www.gutenberg.org/files/31596
Applied Design for Printers, by Harry Lawrence Gage https://www.gutenberg.org/ebooks/30804
Printing in Relation to Graphic Art, by George French https://www.gutenberg.org/ebooks/54349
The Art & Practice of Typography by Edmund G. Gress https://www.gutenberg.org/ebooks/54476
How to Print by Robert W. Tunis https://www.google.com/books/edition/How_to_Print/hUFFAAAAYAAJ?hl=en&gbpv=1&dq=how+to+print&pg=PA5&printsec=frontcover
How to Print by Robert W. Tunis Download PDF Book
American Line Type BookDownload PDF Book
American Specimen Book of Type StylesDownload PDF Book
Desk Book - Specimens of TypeDownload PDF Book
The American printer : ... instructions for beginners ...
by Thomas MacKellar
Modern printing: a handbook of the principles ... https://catalog.hathitrust.org/Record/100641456
The new typography & modern layouts
by Frederic Ehrlich
The New York Times typographical standards https://catalog.hathitrust.org/Record/006681540
Pittsford's manual for advertisers https://catalog.hathitrust.org/Record/006499398
A practical manual of typography and reference book for printers. https://catalog.hathitrust.org/Record/007691168
Practical printing : A handbook to the art of typography ... https://catalog.hathitrust.org/Record/100108876
Weekly newspaper makeup and typography
by Thomas F. Barnhart
The letter-press printer : A complete guide to the art of printing https://catalog.hathitrust.org/Record/001160988
Printing Made Easy - For Users Of Adanda Printing Machines Download PDF Book
Layout California Case DownLoad PDF
Signpress Operating Manual Download PDF Book
Vandercook Manual Download PDF Book
Kelsey - The Printer's Guide Download PDF Book

In my search for online books, I found this site to have to the best selection: http://digital.library.upenn.edu/books/

The following is a list of the American Type Founders Education Cards

Additional Letterpress Resources

Brian Press - A letterpress Community http://www.briarpress.org/
Boxcar Press - For Letterpress supplies https://www.boxcarpress.com/
Ladies of Letterpress is an international trade organization for letterpress printers and print enthusiasts https://ladiesofletterpress.com/
Letterpress Commons - Sharing letterpress printing knowledge for the common good https://letterpresscommons.com/