Identifying window glass

Crown bullseyes, cylinder sheets, and painted church fragments.

Old window glass was made two ways: crown (spun into a disc — slightly curved sheets, concentric ripple, and the thick central 'bullseye' where the pontil attached) and cylinder/broad glass (blown as a cylinder, slit and flattened — straighter ripple, elongated bubbles).

Medieval window glass weathers to an opaque crust and may carry grisaille painting or silver stain (yellow) — painted fragments near a church or abbey site are significant and should be reported. Lead came fragments (H-sectioned strips) are the skeleton of such windows and a find type of their own.

Thickness, tint, bubble shape, and surface ripple separate old glass from modern float glass (which is perfectly flat and flawless). Record thickness, colour, any paint, and edge features like grozed (nibbled) edges that show medieval cutting.

From the guide library inside Collectors Catalogues, a free app for cataloguing antiques and finds with honest, museum-grade records.

More on glass

Identifying ancient glass — Iridescence, bubbles, and weathering.

Dating glass wine bottles — From onion to cylinder — bottle shape is a timeline.

Identifying trade and glass beads — Drawn, wound, and chevron beads that travelled the world.

Identifying Roman glass — Blue-green vessels, ribbed bowls, and iridescence earned underground.

Identifying vessel glass fragments — Wine glass stems, phials, and the anatomy of broken glassware.

Identifying inkwells, stoppers, and small glass objects — The little glass things that survive whole.

Home · Get the app · Guides · Museums · Privacy · Terms