Access became available with the Codex Sinaiticus Project, which exposed features that show that it is a modern manuscript, tampered, between 1844 and 1859.
This is Helen Shenton as well, I recommend from 2:50 to 3:30.
On the 5th of July 2009, I (Helen Shenton) was one of only three people alive who had seen that text, the Codex Sinaiticus, in all four locations...
Helen Shenton is Librarian and College Archivist at Trinity College Dublin.
Collaboratories and bubbles of shush how libraries are transforming
Helen Shenton - TEDxDublin
https://www.youtube.com/watch?v=pHdlWQ28gE8
We are often given harumphs about how the independent scholars must have seen the main two sections of Sinaiticus. There is no indication that any independent (or even non-independent) textual or palaeographic scholars has had access to the two main sections, and compared even the simplest of features, the colour. Nor have they commented on the suppleness, the "phenomenally good condition", the lack of oxidation and foxing, and other elements that would raise the issue of the actual age of the manuscript.
As far as we can tell, the scholars have worked off the tampered facsimile of Tischendorf, and the 2010 Hendricksen Sinaiticus facsimile book also had the colour "smoothed" to hide the distinction of the CFA from the larger section.
No printed book can ever show you the suppleness of the manuscript. That is why we also recommend viewing the video of the pages being turned, lightly and simply, put out by the British Library.
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Steven Avery