MLA

Walpole, Horace, 1717-1797, artist. Birkhead in Kings Vale royal sable, 3 garbs or a border argent [Arms of Derehaugh]. [art original]. [not after 1797]. https://collections.library.yale.edu/catalog/33207391.

APA, 6th edition

Walpole, Horace, 1717-1797, artist. ([not after 1797])[Birkhead in Kings Vale royal sable, 3 garbs or a border argent [Arms of Derehaugh]. [art original]]. https://collections.library.yale.edu/catalog/33207391.