Abstract: Resistor compositions for producing a resistor for use in resistor-incorporated spark plugs and comprising a glass, an inorganic aggregate, and carbon black and/or a carbonaceous substance as a regulating agent for resistance value, with or without a stabilizing agent for resistance under load of the resistor, are now modified by addition of a reducing metallic powder such as powder of Al, Mg, Zn, Sn, Ti, Zr, Fe, Ga and Ag or alloys thereof, to improve the service life characteristics under load of the resistor. Such compositions are further modified by additional presence of a ceramic aggregate of a particle size of 100 to 800 .mu.m, to improve the electric wave noise-preventing property.

Abstract: A resistor composition for a resistor-incorporated spark plug, composed of glass, an inorganic aggregate and carbon, and adapted to be sealed in a centerbore in a ceramic insulator, at least 1% by weight of said aggregate being in advance mixed and calcined with an organic carbonaceous material to adsorb resultant carbonized carbon.

Abstract: A resistor composition for spark plugs comprises 100 wt parts of base mixture of 30-70 wt glass frit with the balance being an inorganic aggregate, 0.1-10 wt parts of carbonaceous material calculated as carbon, 0-30 wt parts of stabilizing agent for resistance under load and 0.1-15 wt parts of boron, boric acid and/or a borate. This composition reduces pores on sealing.

Abstract: A resistor composition for resistor-incorporated spark plugs, substantially consisting of 100 parts of a base mixture consisting of 30 to 70% of glass frit and the balance of inorganic aggregate; 0.1 to 7.0 parts, calculated on carbon upon sintering, of a carbonaceous material; and 0 to 30 parts of an agent for stabilizing resistance of the resistor under load, the glass frit containing 10 to 100% of lead glass having a PbO content of 30 to 88% and a softening point of 300.degree. to 600.degree. C. with the balance of a glass having a softening point exceeding 500.degree. C., each by weight ratio.