Open access distributed with no fees to author and reader
Diamond open access refers to academic texts (such as monographs, edited collections, and journal articles) published/distributed/preserved with no fees to either reader or author. Alternative labels include platinum open access, non-commercial open access, cooperative open access or, more recently, open access commons. While these terms were first coined in the 2000s and the 2010s, they have been retroactively applied to a variety of structures and forms of publishing, from subsidized university publishers to volunteer-run cooperatives that existed in prior decades.
In 2021, it is estimated that between 17,000 and 29,000 scientific journals rely on a diamond open access model. They make up 73% of the journals registered in the Directory of Open Access Journals and 44% of the articles, as their mean output is smaller than commercial journals. The diamond model has been especially successful in Latin America-based journals (95% of OA journals) following the emergence of large publicly supported platforms, such as SciELO and Redalyc. However, Diamond OA journals are under-represented in the major scholarly databases, such as Web of Science and Scopus. It is also noteworthy, that high-income countries "have the highest share of authorship in every domain and type of journal, except for diamond journals in the social sciences and humanities".
In 2022, new national and international policies, such as the UNESCO recommendation on open science, and the "Action Plan for Diamond Open Access" promoted by the cOAlition S aim to support the development of non-commercial or community-driven forms of open access publishing.
Context and definition.
Historical roots of diamond models: knowledge clubs and commons.
Until the Second World War, academic publishing was mostly characterized by a wide range of community-driven scholarly structures with little concern for profitability. Most journals of the 19th century and the first part of the 20th century were collective initiatives led by a scientific movement or institution that largely relied on informal community norms rather than commercial regulations. These historical practices have been described as a form of knowledge commons, or, more specifically, as a "knowledge club" that holds an intermediary status between a knowledge commons and a private company: while managed by a community, journals are mostly used to the benefit of a selected set of authors and readers.
In Western Europe and North America, direct ownership of journals by academic communities and institutions started to wane in the 1950s. The expansion of scientific publishing in the context of "big science" led to a perceived "crisis" of the historical model of scientific periodicals. Between 1950 and 1980, the new model of large commercial publishers came to dominate numerous fields of scientific publishing in western countries:
 ;templatestyles src="Template:Blockquote/styles.css" / ;The small society presses, struggling to cope with growing scale, were supported and then largely supplanted by the 'Big 5' commercial presses: Elsevier (which acquired Pergamon in 1991), Wiley, Springer, Taylor &amp; Francis and Sage. These newly-empowered players brought an industrial approach to the publication and dissemination process, for the first time realising the benefits that these specialised capital and skills could provide by operating at a scale that was unprecedented to that date.
This transformation had wide-ranging consequences over the way scientific journals were managed, not only at the economic but also at the editorial level with an increased standardization of publishing norms, peer-review process, or copyrights. Yet it was neither global nor general, and communal forms of journal ownership and management remained significant in large geographic areas (like Latin America) and in several disciplines, especially in the humanities and the social sciences.
Development of "grassroots" open access (1990–2010).
The open access movement emerged both as a consequence of the unprecedented access afforded by online publishing and as a reaction against the large corporate model that has come to dominate scientific publishing since the Second World War and the hyper-inflation of subscription prices. The early pioneers of open access electronic publishing were non-commercial and community-driven initiatives that built up on a trend of grassroot publishing innovation in the social sciences and the humanities:
 ;templatestyles src="Template:Blockquote/styles.css" / ;In the late '80s and early '90s, a host of new journal titles launched on listservs and (later) the Web. Journals such as "Postmodern Cultures", "Surfaces", the "Bryn Mawr Classical Review" and the "Public-Access Computer Systems Review" were all managed by scholars and library workers rather than publishing professionals.
Specialized free software for scientific publishing like Open Journal Systems became available after 2000. This development entailed a significant expansion of non-commercial open access journals by facilitating the creation and the administration of journal websites and the digital conversion of existing journals. Among the journals registered in the Directory of Open Access Journals (DOAJ) without an article processing charge (APC), the number of annual creation has gone from 100 by the end of the 1990s to 800 around 2010, and has not evolved significantly since then.
Debates over the identity of the open access commons (2003–2012).
In the early debates over open access, the distinctions between commercial and non-commercial forms of scientific publishing and community-driven or corporate-owned structures seldom appear, possibly due to the lack of viable business model for open access. Open access publications were rather increasingly categorized into two different editorial forms: open access articles made immediately available by the publisher and pre-published articles hosted on an online archive (either as a pre-print or post-print). Starting in 2003, the ROMEO project started to devise a color-code system to better identify the policy of scientific publishers in regard to open sharing of scientific articles, from "yellow" (pre-print only) to "green" (no restriction in place): "the 'greenest' publishers are those that allow self-archiving not only of the author's accepted manuscript, but of the fully formatted and paginated publisher PDF". In 2004, Harnad et al. repurposed this classification scheme into a highly influential binary scale: articles directly made available by the publisher belong to "gold" open access (instead of "yellow") and online archives are defined as "green" open access. With this breakdown of open access into "green" and "gold", there is no distinction between commercial and non-commercial publishers. For Peter Suber the "gold" model embraces both journals supported by APCs or by other means of funding, as well as volunteer-run journals: "In the jargon, OA delivered by journals is called gold OA, and OA delivered by repositories is called green OA."
Tom Wilson introduced the expression "Platinum Open Access" in 2007 following an heated debate with Stevan Harnad and other open access activists on the "American Scientist Open Access Forum" mailing list. On his blog, Wilson defended the necessity of enlarging the classification of open access publishing forms as well as stressed the danger of conflating commercial and non-commercial open access journals.
 ;templatestyles src="Template:Blockquote/styles.css" / ;[The "gold" and "green" classification] is not really the whole story and is in danger of perpetuating the myth that the only form of open access publishing is that made available through the commercial publishers, by author charging. This is why I distinguish between open access through author charging, which is what the Gold Route is usually promoted as being (…) and the Platinum Route of open access publishing which is free, open access to the publications and no author charges. In other words the Platinum Route is open at both ends of the process: submission and access, where as the Gold Route is seen as open only at the access end.
The term "diamond open access" was coined later in 2012 by Marie Farge, a French mathematician and physicist and open access activist. Farge was involved in the Cost of Knowledge campaign led by Timothy Gowers against the excessive cost of scientific publishing. The reference to "diamond" was a hyperbolic pun on the "gold" metaphor that aims to suggest that non-commercial/free model were ultimately the best: "I have proposed to call this third way 'Diamond OA' by outbidding the 'Gold OA' terminology chosen by the publishers". "Free OA" was also contemplated as an alternative name.
The "Forum of Mathematics", an open access journals co-created by Timothy Gowers, was the first publication to explicitly claim to be a diamond journal: "For the first three years of the journal, Cambridge University Press will waive the publication charges. So for three years the journal will be what Marie Farge (who has worked very hard for a more rational publication system) likes to call diamond open access, a quasi-miraculous model where neither author nor reader pays anything".
Defining the diamond model (2012–…).
In 2013, Fuchs and Sandoval published one of the first systematic definition of diamond open access: "Diamond open access Model, not-for-profit, non-commercial organizations, associations or networks publish material that is made available online in digital format, is free of charge for readers and authors and does not allow commercial and for-profit re-use." This definition is associated to a controversial stance against the leading definition of gold open access: "We argue for differentiating the concept of Gold Open Access Publishing because Suber and others mesh together qualitatively different models, i.e. for-profit and not-for-profit ones, into the same category, whereas others, especially policy makers, simply forget or exclude not-for-profit models that do not use author fees or reader fees." The debate over the relationship between "diamond" or "platinum" open access publications with "Gold" open access has never settled and remains a point of contention in 2021, even after the publication of the OA Diamond Study. While valuing the study, Martin Paul Eve still consider diamond open access as a "category error".
Since 2013, the theoretical literature on the diamond model has been increasingly influenced by the institutional analysis of the commons. Consequently, the "Open access commons" has recently emerged has an alternative label, although it is less used in a descriptive way and more as a programmatic ideal for the future of non-commercial open access. The conclusion of the "OA Diamond study" calls for the realization of The OA Commons as "a diverse, thriving, innovative and more interconnected and collaborative OA diamond journal ecosystem that supports bibliodiversity and serves many languages, cultures and domains in the future.". Similarly, Janneke Adema and Samuel Moore have proposed to "redefine the future of scholarly publishing in communal settings" through a "scaling small" that ensure the preservation and development of diverse editorial models.
Analysis of the diamond model has been significantly deepened by the commission of large scale empirical studies such as the "OA Cooperative Study" (2016) by the Public Knowledge Project or the "OA Diamond Study" (2021) by the cOAlition S. Noteworthy, the 2021 study found:
Distribution.
The "OA Diamond Study" gives an estimation of ;29,000 diamond open access journals in 2021 which represent a significant share of the total number of scholarly journals. Diamond journals make up for 73% of the open access journals registered on the Directory of Open Access Journals (DOAJ) with 10,194 entries out of 14,020 in September 2020. In 2013, Fuchs and Sandoval already noted that, as a far as the number of individual journals is concerned, diamond open access is the main form of open access publishing: "Diamond open access is not just an idea, but rather, as the empirical data provided in this paper shows, the dominant reality of open access."
While the diamond model is prevalent among open access journals when looking at the journal titles, this is not the case when looking at the aggregated number of articles, as they publish less articles overall. The "OA Diamond Study" finds that the 10,194 journals without publication fees registered on the Directory of Open Access Journals published 356,000 articles (8–9% of all scholarly articles) per year from 2017 to 2019 instead of 453,000 articles (10–11%) published by 3,919 commercial journals with APCs. This discrepancy can be mostly attributed to a consistently lower output of diamond open access journal in comparison with commercial journals: "In DOAJ we find that the majority of OA diamond journals (54.4%) publish 24 or fewer articles per year; only 33.4% of APC-based journals have a similar size." Diamond journals also have a more diverse editorial production, which includes other forms of scholarly productions like book reviews or editorials, which may contribute to decreasing their share in the total number of research articles.
From 2014 to 2019, the output of diamond open access journal has continued to grow in absolute terms, but has decreased relatively to the output of commercial open access journals. The period showed a significant development of APC-based large publisher as well as an increasing conversion of