How was this made?
This object is made entirely of limestone. While stone can be salvaged and reused from torn down buildings, new stones are extracted by quarrymen from mines. Limestone was the building stone of choice, since it was a very strong piece of rock that was not easily damaged. High skilled laborers such as stone-cutters and stone masons would be at the cathedral construction sites to cut specific shapes and carve designs into the limestone. Stonemasonry was not an easy trade, since making elaborately detailed sculptures using a mallet and chisel was an extremely time consuming task that required precision and attention-to-detail. The roundel, with its very intricate designs and 'drill-like' work in the border indicates that a very skilled stone mason worked on this piece.
Here is a video on how stone masons carved out their sculptures:
In addition to the very distinct limestone materiality is the surprising unknown detail of polychromy. There is evidence of paint in the griffin's eye and near the wing, suggesting that the roundel was a dazzling vermilion in color. This 'splash' of color was another hint of Romanesque influence, as Roman architecture often had a combination of colored marbles and metals that would work together to illuminate the piece. Additionally, early Byzantine architecture favored general polchromacity, which gave the objects light-bearing qualities that would create effects of glitter and brilliance. This technique was most likely replicated in the roundel to not only pay homage to early Byzantine architecture but to illuminate the griffin as though it were a divine being.