The big 'problem' as opposed to coins is that virtually all lead
seals, by their nature, are extremely
rare. This means there is usually not much overlap between the various references, which means you will pretty much need all of them...! That being said, there are some that are a
good place to start. Towering above all is the
Zacos collection, published in 2 volumes of 4 parts text and 2 parts of plates.
Vol. 1 is mainly 6th-9th centuries and is the best reference for that period.
Vol. 2 is roughly 10th to the fall of
Constantinople. These are beautifully published books. Next to those, the DO series on
seals is a
good place to start. Another considerable series is Laurent's
work in
his Corpus on
seals of the Administration and the
Church (he did not
complete the
Military). THen there is Jordanov's 3
part corpus on
Bulgarian seals. And a great introduction to
seals in
German is Seibt's 1st
part on
seals in
Vienna (Byzantininischen Bleisiegel in Österreich I).
Regards
Gert