Mosaics such as these, aside from being important and beautiful works of art, can be particularly interesting for examining the elements of early liturgical practice, vestments, architecture, and so on that can often be within them.
Case in point, a quick view of the famed 6th century Justinian mosaic in San Vitale in Ravenna shows a detail which would certainly appear to be a thurible in its uncapped form. Compare this, for example, to the uncapped Ambrosian thurible.
