1. A method of sealing a metal element in an open end of a tube of glass, which method comprises the steps of inserting the element partially within the tube through the open end, applying heat to an area of the glass of the tube adjacent the open end of the tube until the glass starts to soften and flow toward the element to start the seal, and producing a displacement between the tube and the area of application of the heat to move the area of application of the heat to the glass toward the end of the tube as the glass softens so that the heat is applied to an area at the outer end of the seal.

2. A method of sealing a metal element in an open end of a tube of infrared absorbing glass, which method comprises the steps of inserting the element partially within the tube through the open end, directing infrared energy on an area adjacent the top of the tube until the glass softens and starts to flow toward the element to form a seal, reflecting infrared energy onto an area adjacent the top of the tube to supplement the directed energy, and producing relative movement between the tube and the reflected energy to move the reflected infrared energy toward the end of the tube as the seal starts to form to concentrate the infrared energy on the area of the glass that forms the top of the seal.