Dennis five printed recommendations are as follows:
F.H. Marshall, Catalogue of the Finger Rings: Greek, Etruscan and Roman, in the departments of antiquities, British Museum. Originally published in 1907. Pictures are tiny & grainy but a ton of examples with accompanying descriptions
O.M. Dalton, Catalogue of the Finger Rings, Early Christian, Byzantine, Teutonic, Medieval and Later ..... In The Museum British Museum. Another standard reference, this one from 1912
Friedrich Henkel, Die römischen Fingerringe der Rheinlande und der benachbarten Gebiete. Roman rings from Germany. Published in 1913. Grainy pictures again and text is in German
1913
T.N. Pollio, Ancient Rings: An Illustrated Collector’s Guide. A good modern compilation of common finger rings from the Bronze Age to early Modern Period. Available in paperback and eBook from Amazon
T.N. Pollio, The Art of Medieval Jewelry: An Illustrated History. Another profusely illustrated modern study of common finger rings from the 6th to 16th century. Also available from Amazon
Gaius