The diamond magazines they are open access journals that do not charge either the authors or the readers but are subsidized by scientific societies, universities, etc. Therefore, they have no financial barriers either to access or to publish. This model is attractive to researchers and funding institutions, as it meets current requirements for transparency and free access to research.
An Coalition S indicates that there are more than 29.000 diamond magazines worldwide (2021 data) and a little less than half, today more than 13.000 are registered in DOAJ: Directory of Open Access Journas a. With the option Journto those without fees DOAJ is one of the most useful tools for finding this type of publication.