The most traditional ways to achieve open access are the Green and Gold, established in the Budapest Declaration. Subsequently other variants have emerged such as the Bronze or Diamond routes.
The Green route, or self-archiving route, is based on the practice of depositing previously published articles in an open access repository. The repository can be institutional, thematic (e.g. arXiv), or general (e.g. Zenodo). A publication can be deposited in more than one repository.
Advantages: The author does not pay to deposit their publication in open access, since most of the repositories are public and free.
Disadvantages: Academic publishers often require authors to transfer the copyright of their publication for a specified period of time, called an embargo. Therefore, the authors cannot make the full text public until the embargo imposed by the publisher has been fulfilled. Each journal has its own copyright transfer policies. These set the self-archiving capacity of the authors and the permissions regarding which versions of the articles can be deposited in a repository. The editorial policies of academic journals can be consulted in the SHERPA/RoMEOdatabase.
The Gold route consists of the editor of a journal publishing the articles in open access immediately and permanently, under a licence where the author maintains the copyright. Journals usually require a payment for publication costs, the so-called APCs (article processing charges).
The journals that allow the Gold route maybe open access journals or hybrid journals, i.e., journals where the access is via subscription but offer authors the option of publishing the final version of their article immediately - upon payment - in open access.
Advantages: The author retains the copyright of their publication and can immediately share and make their work accessible.
Disadvantages: Publishing costs are usually quite high. These must be borne by the authors themselves or by their institutions.
The Bronze route refers to articles that are free to read on the editors’' pages, but without an explicit open licence that allows their distribution and reuse.
The Diamond or Platinum route refers to journals that publish in open access, and that do not charge either the authors for publishing or the readers for reading. These journals are generally funded either by academic and government institutions, or by scientific societies.