Green, Gold en Diamond open access
There are two ways of achieving open access, via the gold route and the green route (Harnad et al., 2008). The gold route works through publication, via a publisher platform, in open access journals. This route is in most cases not free. The publication costs, known as ‘article processing charges’ (APCs), are paid by the author or his or her institution. Some organizations that fund academic research demand that resulting publications are published in open access. Sometimes they are willing to cover the costs. A list of open access journals that are accessible worldwide can be found on the DOAJ website (“Directory of Open Access Journals,” 2018). Universities and their libraries are having more and more agreements with big publishers in which they arrange the possibility for their academic staff to publish in open access for free or with a discount.
Via the green route the full text of academic publications is deposited in an institutional repository, a publicly accessible database managed by a research institute e.g. a university. Mostly the pre- or postprint of research publications are made open access in this way.
The last couple of years scientists from different fields took the initiative to arrange so-called ‘overlay journals’: digital journals linking to peer reviewed articles on a preprint server. Discrete Analysis, a mathematical overlay journal, is an example of this (Ball, 2015). This is completely ‘diamond open access’, meaning no charges for the reader or the author (Fuchs & Sandoval, 2013).