This is a monochrome photograph taken of Hoffman's 14 set designs for Wagner's <i>Der Ring des Nibelungen</i> opera in 1876.  Hoffman authorized Angerer to publish and sell copies of the photographs.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[1]</a></sup>
<bdi><a href="https://www.wikidata.org/wiki/Q18508704" class="extiw" title="d:Q18508704"><span title="Austrian photographer">Viktor Angerer</span></a>
</bdi>
<cite style="font-style:normal">Johnson, Diane Chalmers (Winter 1994). "<a rel="nofollow" class="external text" href="https://www.jstor.org/stable/3109160">Siegfried and the Rhine Maidens—Albert Pinkham Ryder's Response to Richard Wagner's Götterdämmerung</a>" (PDF). <i>American Art</i> <b>8</b> (1): 26. Illinois, United States: University of Chicago Press. <a href="https://en.wikipedia.org/wiki/International_Standard_Serial_Number" class="extiw" title="en:International Standard Serial Number">ISSN</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/issn/1073-9300">1073-9300</a>. Retrieved on <span class="mw-formatted-date" title="2011-06-23">2011-06-23</span>.</cite>