Ford's Quick Defrost Windshield/Rear Window option was first introduced in 1974 on two of its top of the line prestige cars, the Ford Thunderbird and Continental Mark IV. Using the same space age technology as the Boeing 747 electrically heated windshield. A transparent, thinly coated gold-bearing metallic film is sandwiched between layers of polyvinyl butyral and glass. When electrical current is applied to this film, it warms quickly and evenly to rapidly clear the glass of frost or ice. A second alternator is provided on cars equipped with this option, and two defrost power levels were provided: high for initial fast clearing, and low to keep the glass clear. After three to four minutes of operation, the glass areas are mostly cleared. One characteristic of this glass is its distinctive gold tint, clearly visible from outside the car, but barely perceptible from within. In addition to fast defrosting, this film layer laminated within the layers of glass rejects non-visible solar heat, which improves air conditioning performance during the warmer months. Known in the glass industry as the DW825 windshield, this option was short lived due in part to its cost, which was $306.70 on the Mark IV in 1974, and peaked at $360 on that same model in 1976.