Depending on the “site” (repository or journal) and the time of dissemination, authors can choose different routes for Open Access publication or dissemination.
With Green Open Access, authors self-archive their own work (full text and descriptive metadata) free of charge, with a possible embargo and in the version(s) permitted by the policies of the publisher with whom they have signed the publishing contract (Copyright Transfer Agreement), in a specific institutional, subject-specific or generic archive.
On the other hand, the work -in accordance with the Gold Open Access (Gold OA model)- is made available in open access by the publisher itself immediately, after payment of a publication fee (Article Processing Charges APC) by the author or the institution s/he belongs to.
Finally, Diamond Open Access is practised if the work is published, without the payment of editorial fees by the author, by academic institutions, research bodies, non-commercial/non-profit organisations that make it directly, freely and immediately accessible to readers.
The opportunity to introduce the Diamond Route (by Christian Fuchs and Marisol Sandoval in 2013), previously referred to as Platinum (by Tom Wilson in 2007), emerged in the Open Access movement when the Gold Route began to include commercial hybrid journals on a massive scale. Therefore, some representatives of the Open Access world proposed renaming the (Full) Gold model – which originally did not involve commercial purposes or the payment of publication fees (APCs) – as Diamond (or Platinum), and at the same time redefining the scope of the (Full) Gold model, now also including the original Red (or Hybrid) Road (partial Open Access publication for commercial purposes and only with APCs).
In terms of content, a Full Gold journal contains only Open Access articles.
A journal is considered hybrid when, alongside articles that are traditionally only accessible by subscription and therefore closed access, authors can request immediate open access dissemination of their articles upon payment of publication fees (APCs).
Hybrid journals are therefore funded by both subscriptions and publication fees (double dipping), with double charging for subscribers and authors. Publishing in hybrid journals is sometimes not considered consistent with the open access mandate. Currently, Horizon Europe excludes articles in hybrid journals from reimbursement, but these can be funded by Transformative Agreements between the publisher and the affiliated institution.
Finally, an article follows the Bronze Route if it is made available for reading only on the publisher's website, often without a specific reuse licence to guide the reader.
Based on reuse rights, a distinction is made between Open Access, libre and free.
In free Open Access, only economic barriers are removed (no subscription, no publication fees, no purchase costs for individual articles), but legal reuse barriers remain.
Open access libre, on the other hand, removes both economic barriers and certain restrictions on reuse, mostly indicated by specific Creative Commons licences, according to the Open Access models defined by the Budapest Open Access Initiative, the Bethesda Statement on Open Access Publishing and the Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities.
The Green Road can be free (mostly) or libre.
The Gold Road can be free (mostly) or libre.
For further information:
Diamond open access. Wikipedia.
Kelly, J. M. (2013). Green, Gold, and Diamond? A short primer on Open Access.