Burnham, S.M.: Precious Stones in Nature, Art and Literature (1886): p. 163
Westropp, H.M.: A Manual of Precious Stones and Antique Gems (1874): p. 104
Unknown: 422.16
Comments: BURNHAM: 'THE ONYX WAS FREQUENTLY ENGRAVED, A REMARKABLE SPECIMEN BEING AFFORDED BY THE CORINTHIAN HELMET ON JASPER-ONYX. AN IMITATION OF THIS ENGRAVING CONSTITUTED THE CHEF-D'?UVRE OF THE NOTORIOUS PONIATOWSKY COLLECTION.'