And from our beloved Wikipedia:
In the 16th century Western scholars became aware of the manuscript as a consequence of the correspondence between Erasmus and the prefects of the Vatican Library, successively Paulus Bombasius, and Juan Gin口s de Sep口lveda. In 1521, Bombasius was consulted by Erasmus as to whether the Codex Vaticanus contained the Comma Johanneum, and Bombasius supplied a transcript of 1 John 4:1-3 and 1 John 5:7-11 to show that it did not. Sep口lveda in 1533 cross-checked all places where Erasmus’s New Testament (the Textus Receptus) differed from the Vulgate, and supplied Erasmus with 365 readings where the Codex Vaticanus supported the latter, although the list of these 365 readings has been lost. Consequently, the Codex Vaticanus acquired the reputation of being an old Greek manuscript that agreed with the Vulgate rather than with the Textus Receptus. Not until much later would scholars realise it conformed to a text that differed from both the Vulgate and the Textus Receptus - a text that could also be found in other known early Greek manuscripts, such as the Codex Regius (L), housed in the French Royal Library (now Bibliotheque nationale de France). …]
Before the 19th century, no scholar was allowed to study or edit the Codex Vaticanus, and scholars did not ascribe any value to it; in fact it was suspected to have been interpolated by the Latin textual tradition. John Mill wrote in his Prolegomena (1707): “in Occidentalium gratiam a Latino scriba exaratum” (written by a Latin scribe for the western world). He did not believe there was value to having a collation for the manuscript. Wettstein would have liked to know the readings of the codex, but not because he thought that they could have been of any help to him for difficult textual decisions. According to him, this codex had no authority whatsoever (sed ut vel hoc constaret, Codicem nullus esse auctoris). …]
In 1809 Napoleon brought the manuscript as a victory trophy to Paris, but in 1815 it was returned to the Vatican Library. During that time, in Paris, German scholar Johann Leonhard Hug (1765-1846) saw it. Hug examined it, together with other worthy treasures of the Vatican, but he did not perceive the need of a new and full collation.
Cardinal Angelo Mai prepared the first typographical facsimile edition between 1828 and 1838, which did not appear until 1857, three years after his death, and which was considered unsatisfactory. …] In 1843 Tischendorf was permitted to make a facsimile of a few verses, in 1844 Eduard de Muralt saw it, and in 1845 S. P. Tregelles was allowed to observe several points which Muralt had overlooked. He often saw the Codex, but “it was under such restrictions that it was impossible to do more than examine particular readings.”
“They would not let me open it without searching my pockets, and depriving me of pen, ink, and paper; and at the same time two prelati kept me in constant conversation in Latin, and if I looked at a passage too long, they would snatch the book out of my hand”.
Tregelles left Rome after five months without accomplishing his object. During a large part of the 19th century, the authorities of the Vatican Library obstructed scholars who wished to study the codex in detail. Henry Alford in 1849 wrote: “It has never been published in facsimile (!) nor even thoroughly collated (!!).”Scrivener in 1861 commented:
“Codex Vaticanus 1209 is probably the oldest large vellum manuscript in existance, and is the glory of the great Vatican Library in Rome. To these legitimate sources of deep interest must be added the almost romantic curiosity which has been excited by the jealous watchfulness of its official guardians, with whom an honest zeal for its safe preservation seems to have now degenerated into a species of capricious wilfulness, and who have shewn a strange incapacity for making themselves the proper use of a treasure they scarcely permit others more than to gaze upon”. It (…) “is so jealously guarded by the Papal authorities that ordinary visitors see nothing of it but the red morocco binding”.
Thomas Law Montefiore (1862):
“The history of the Codex Vaticanus B, No. 1209, is the history in miniature of Romish jealousy and exclusiveness.”
Burgon was permitted to examine the codex for an hour and a half in 1860, consulting 16 different passages. Burgon was a defender of the Traditional Text and for him Codex Vaticanus, as well as codices Sinaiticus and Codex Bezae, were the most corrupt documents extant. He felt that each of these three codices “clearly exhibits a fabricated text 口 is the result of arbitrary and reckless recension.” The two most widely respected of these three codices, 口 and B, he likens to the “two false witnesses” of Matthew 26:60.