In 1845 Charles Knight of London published
Mary Cowden Clarke's The Complete Concordance to Shakespere: Being a Verbal Index to All the Passages in the Dramnatic Works of the Poet. This large octavo volume consisted of 860 pages set in three columns of minuscule 6 point non pareil type, making reading anything in it a significant challenge. My suspicion is that this was one of the few books of such length ever set in such tiny type. Nevertheless the work replaced prior concordances to Shakespeare, and was reprinted, undoubtedly from stereotype plates, several times through the 1880s. It was published in
New York by Wiley and Putnam in 1846.
According to the Wikipedia, the work occupied Mrs. Cowden Clarke 16 years, of which 12 years were involved with the compilation, and no less than four years in production of the book. Undoubtedly typesetting and proofreading such an enormous and very complicated manuscript in such tiny type was a severe challenge both in vision and manipulation of the tiny pieces of type for manual typesetters. Those typesetters who could undertake such a project undoubtedly required magnification to get the work done unless they were severely nearsighted. Presumably Knight insisted on such small type in order to hold the costs down, but it also appears that the typesetting challenge was beyond the capabilities or the desires of Knight's usual printers, Wm Clowes, and the work was typeset and printed by Manning and Mason, who are credited in 6 pt type at the foot of the title page and on the final leaf of text. The work was published in monthly parts during 1845, after which copies were sold bound in publisher's cloth. My copy is in the original cloth binding.

Jeremy Norman Collection of Images - Creative Commons
This copy of Cowden Clarke's concordance has been recased in its original cloth binding.

Jeremy Norman Collection of Images - Creative Commons

Jeremy Norman Collection of Images - Creative Commons