Last Updated: Dec 11, 2016 Views: 28
A "witch ball" is a basic bubble of glass, usually blown at the furnace.
I haven't found explicit instructions for creating them; however, the following books illustrate the initial steps for blowing a bubble in glass. (Please see the attached bibliography for more information)
Burke, Glassblowing: A Technical Manual.
McKelvey, James. The Art of Fire: Beginning Glassblowing.
Schmid, Edward T. Beginning Glassblowing.