No glass in Britain, except beads, pre-dates the Roman Iron Age. I’m not completely certain whether in the Iron Age glass was actually made from its basic ingredients in Britain (as opposed to simply worked) or if it was all imported from the Roman world. The classic example of Iron Age bead making was at Meare in Somerset where some 295 glass beads were found, mainly Guido 10 Meare spirals and variants which I have illustrated with an image from her great book. There are no exact European parallels. After the incorporation of Britain within the empire it was exposed to the products of the 1st-3rd century AD glass workshops which were common in legionary fortresses and the larger towns of the Rhineland: Treves, Bonn, and Cologne. Scholars are virtually certain that all Roman glass was originally made in huge tanks in the eastern Mediterranean, and then exported all over the empire as lumps for re-melting and working. In the 3rd – 4th century there was a switch to a type of glass called HIMT. This was high in iron, manganese and titanium. These ingredients were not added deliberately but simply reflect the use of a different quality of sand in a new glass-making site, possibly Egyptian. After the Roman period the presumption is that no new glass came from the Mediterranean area. The presence of metals, like copper and lead, in the glass of this period strongly suggests the recycling of coloured glass mosaics from Rome and N. Africa. Similar material was re-used for beads in Scandinavia.
The only ancient glass beads I have actually found myself are examples of a plain, yellow, flattened, annular yellow glass bead recovered from the broch village excavation at Old Scatness in Shetland. As they emerge, damp from soil residues, they are a brilliant, luminous, yellow colour but this fades somewhat as the beads dry. A bead of this type is also pictured. Compositional analysis has identified two distinct British opaque yellow bead-making traditions; one originating in the 5th-2nd century BC in southern Britain, and the other in 1st-2nd century AD Scotland. The densest clusters are from Meare, Somerset and Culbin Sands, Moray, which may have been bead-making production sites for the two traditions. Scatness yellow beads are classified as Guido Class 8. Beads of this type have also been identified at other Northern Isles locations, and also broch and wheelhouse sites in the Western Isles, and Scottish mainland. Plain undecorated beads are notoriously difficult to date but in the case of this bead the yellow pigment is crucial. Before the 4th century AD opaque yellow glass production was based on the use of antimony oxides. The production of yellow glass with crystals of lead-tin oxide (lead stannate – PbSnO4) occurs first in late antiquity. Opaque yellow glass appears to have been produced by adding pre-formed pigment to a soda-lime-silica glass. Evidence of such glass working has been found at several sites one of which is in an assemblage of early medieval glass-working waste from Tarbat near Inverness. The belief is that the lead and tin oxides were heated together and these reacted with the fabric of the crucible to form crystals of the lead-tin oxide in a lead-silica glass. This was then mixed with soda-lime-silica glass. It is uncertain whether the yellow pigment was made locally or imported but evidence for its manufacture exists in Germany.