heat sources moreover microwave energy may be used as well fig1 generally illustrates a controlled focused infrared cfir source 700 which may be used in both the preheating of the sheet prior to receiving the gasket as well as heating with or without the application of pressure after the sheet and gasket contact each other cfir 700 includes one or more infrared emitter assemblies 702 such as model 5305 104 made by radiant energy research inc of minneapolis minn and disposed above sheet 722 in a pattern conforming to that region of sheet 722 adapted to receive gasket 732 in the alternative a single infrared emitter assembly may be moved above sheet 722 by a guided robotic arm in a pattern conforming to that area to receive gasket 732 computer process controller 704 preferably causes infrared emitter assembly 702 to emit infrared energy into sheet 722 from a side opposite that containing frit coating 730 and primer coating 748 although it may also be directed from the same side as the frit layer 730 and primer 748 a spectrophotometer 706 coupled to computer process controller 704 detects the energy reflected and radiated from sheet 722 based upon the feedback from spectrophotometer 706 controller 704 adjusts the power of infrared energy emitted by assembly 702 to obtain maximum absorption by frit layer 730 and primer 748 and raise the temperature level to between 100 u00b0 f and 350 u00b0 f although cfir 700 has been described for use in both heating steps it is contemplated that it will be.