MLA

Purcell, E. (Edward), printmaker. The Holy Alliance unmasked [graphic]. [February 1823]. https://collections.library.yale.edu/catalog/33117077.

APA, 6th edition

Purcell, E. (Edward), printmaker. ([February 1823])[The Holy Alliance unmasked [graphic]]. https://collections.library.yale.edu/catalog/33117077.