Electrical resistor and method of production

Claim 1

In a method for producing a spiralled, film type electrical resistor wherein a film of resistance material is deposited on the elongated surface of a glass rod and selected areas of said film of resistance material are removed from said glass rod by exposure to a laser beam, said filmed glass rod and said laser beam being moved relative to one another such that said film of resistance material is removed along a helical path about the periphery of said rod, the improvement which comprises incorporating FeO and/or CuO into the composition of said glass rod in an amount effective to absorb a sufficient amount of said laser beam to prevent damage to said film on the surface of said rod opposite to the surface exposed to said laser beam, said glass rod consisting essentially, in weight percent on the oxide basis, of 10-40% RO, wherein RO consists of at least two of the following oxides in the indicated proportions of 0-11% MgO, 0-12% CaO, 0-10% SrO, and 0-9%, BaO, 10-20% Al 2 O 3 , 0.1-5% FeO and/or CuO, 50-65% SiO 2 , 0-10% B 2 O 3 , 0-3% SnO 2 , and 0-2% As 2 O 5 and/or Sb 2 O 3 .