From: Richard Poynder <[log in to unmask]>
Date: Mon, 23 Mar 2015 15:07:05 +0000

Contrary to what one might expect, not all the items in open access
repositories are publicly available. Estimates of the percentage of
the content in repositories that is not in fact open access tend to
range from around 40% to 60%. This will include bibliographic records
containing only metadata, plus full-text documents that have been
placed on “dark deposit” — i.e. documents that are present in the
repository but not freely available, either because they are subject
to a publisher’s embargo or because the author(s) asked for the
full-text to be deposited on a closed access basis. To enable
researchers to nevertheless obtain copies of items that have been
placed on dark deposit OA advocates developed the request eprint
button. But how does the button work, and how effective is it?

Eloy Rodrigues, Director of Documentation Services at the University
of Minho, discusses the issues and outlines the situation at UMinho
here:

http://poynder.blogspot.co.uk/2015/03/open-access-and-request-eprint-button-q.html