Patent ID: 6857926

Claim:
A method of making an arc tube chamber intermediate tubular end portions comprising the steps of: (a) providing a tube of vitreous material; (b) heating a portion of the tube sufficiently to soften it in a predetermined area; (c) axially compressing the tube to force the softened material in the heated area radially inward and outward around the circumference of the tube to thereby thicken the tube wall in the heated area; (d) repeating step (b) and step (c) in areas of the tube proximate to the previously thickened tube wall at least one additional time to thereby thicken the wall of the tube over an axial distance approximating the length of the desired chamber; (e) heating the thickened wall area of the tube; (f) positioning a mold having a surface defining a chamber cavity of a desired shape over the heated thickened wall area, the chamber cavity defining surface having a portion for defining a canoe-shaped portion of the arc tube chamber; (g) internally pressurizing the tube to expand the heated thickened area of the tube against the internal wall of the mold cavity to thereby form a chamber in the tube; and (h) removing the mold from the chamber to thereby provide an arc tube chamber intermediate open tubular end portions.