Q. What was the process and material recipe used by the Egyptians with regards to 'core forming'?

In David Grose's book, Early Ancient Glass, he describes the core-forming technique: "A removable core of material, probably a combination of clay, mud, sand and an organic binder (but never sand alone), is built up around a metal rod into the shape of the interior space of the desired vessel. The core is then covered in some fashion with hot glass, by dipping, or more probably, by trailing threads of glass over the core as it is rotated. Next, the vessel is repeatedly reheated and marvered rolled on a flat stone slab. Decoration in the form of threads or blobs may then be trailed on each and pressed into the surface by marvering, usually after being combed or dragged with a bronze pin or hook into feather, festoon, upright festoon, zigzag, or other patterns. Unless repeatedly reheated and marvered, vertical indentations caused by the tooling of the threads remain on the body....
"...Rim-disks, handles, lugs, pad-bases and base-knobs are applied separately after further reheating. Once they have been added, it is difficult or impossible to marver the vessel further, and any additional threads applied to the rim, rim-disk, or base are left unmarvered or only partly marvered. In certain instances rims or lugs are drawn out from the body of the vessel."
"The metal rod is then removed and the vessel annealed. Afterward, the core is scraped out, leaving a rough, pitted, often gray or reddish interior surface." p. 31.

Since Grose's book was published in 1989 there has been a great deal of research by archaeologists, scholars and glass artists relating to core-forming.

Dudley Giberson's video and article describe his (generally accepted now) theory that glass frit was picked up on the heated core, then frit was then melted over a small glory hole (instead of winding the glass on the core). Giberson repeatedly picks up frit, heats and marvers it in to create the surface of the vessel. Next decorative threads or blobs are added as Grose describes. Take a look at Giberson's book A Glassblower's Companion for more information.
about the "vertical glory hole."

Contemporary beadmakers and a Japanese glassmaker use steel wool wrapped around a mandrel (you can use fine wire to attach the initital wrap), covered with thin layers of bead release. Several of the resources in our bibliography describe this process.

BH