Theophilus: On Divers Arts otherwise known as a List of various arts(Schedula diversarum artium) or On various arts(De diversis artibus) is a Medieval Treatise detailing various recipes and techniques used in Glass Making, metalwork and painting.
Whilst the Glass Making section primarily covers furnace glass blowing and Stained glass some of the techniques can be used to inform Lampwork.
Theopphilus describes a glass ring making technique that involves using a lance like tool with a hollow metal spike sheathing a wooden handle and a disk guard. This was dunked into a pot containing molten glass removing a small amount. The tool would then be driven hard into a wooden post thus creating a ring hole. The ring would then be struck to loosen it and heated in a flame to make it more circular and by rotating it, it would decent to the disc guard.