Materials published before 1923 are:

Materials published before 1923 are considered to be in the public domain because they have surpassed the copyright protection period that was established in the United States. Generally, works published before 1923 no longer have copyright protection, making them freely available for use by anyone without the need for permission or the payment of royalties.

One key factor behind this determination is that copyright laws have undergone changes over the years, which specified different durations of protection. The Copyright Term Extension Act, for example, extended the term under certain conditions, but works published before 1923 were already in such a state that they do not qualify for any extension, thus entering the public domain.

As a result, these pre-1923 works can be utilized for educational, scholarly, or creative purposes without legal restrictions.