Quoted from AlexF:After years of collecting mainly Gottlieb and Williams machines I thought a perfect original glass was an extreme rarity. Then I picked up a Bow & Arrow with a near perfect glass. Thought I must have gotten lucky until I also got a Flip Flop, Hi-Deal and Night Rider with near perfect glass as well. Wow Bally figured something out during that era.
I thought someone stated at one time Bally used thicker glass. Theory was that it was less prone to expansion and contraction with temperature swings. Not sure if that is true?
The ink expands and contracts. Not the glass.