MLA

[Trial Proof for an Engraved Portrait of an Unknown Man] [Art Original]. 0AD. https://collections.library.yale.edu/catalog/16222774.

APA, 6th edition

[Trial proof for an engraved portrait of an unknown man] [art original]. (0 C.E.). [Trial proofs, Portrait drawings, Graphite drawings British 19th century, Ink drawings British 19th century, Steel engravings England]. https://collections.library.yale.edu/catalog/16222774.