The piece was apparently in a "European private collection" in 1978 and it is being sold by "a U.S. private collector". There are no named owners and no list of previous publications.
The catalogue entry has been prepared with the assistance of Ruth E. Leader-Newby, author of Silver and Society in Late Antiquity (2004) [WorldCat] [review by me in Classical Review].
The patten has clearly been the subject of scientific analysis:
A laboratory report number 93075 issued by Conservation and Technical Services Limited, London, analyzing the condition and method of the manufacture accompanies this lot.Conservation and Technical Services Limited, London describe their services:
Conservation and Technical Services Ltd provide analytical and conservation services to numerous museums and cultural institutions throughout the world as well as for practicing conservators, auction houses, art dealers and collectors.A client list appears on their website.
Where was this piece of ancient silver found? The eastern Mediterranean? Italy? Northern Europe? The catalogue entry keeps the options open: "the stylistic influences of Constantinople and the iconographic influences of Rome itself". There are intellectual consequences for interpreting objects that have no recorded find-spots.