The General Electric Company, which was the first to introduce the asphalt mica flake insulation system about the year 1915, continued to make changes in the materials and final properties of coils insulated with the system into the 1980s. A higher percentage of drying oils were used to make the asphaltic resins employed in both the initial tape construction and in the brushing varnish that was applied between each layer of tape as it was applied. As discussed in Section 3.1, these asphaltic resin variations were weakly thermoset materials when processed through the several shop manufacturing operations. There was, therefore, a 5 to 7 year delay, as compared to the experience of Westinghouse Electric Corporation with the asphaltic mica flake insulation system, before increasing generator ratings and the associated increased slot lengths led to the frequent occurrence of tape separation in generator stator coils.