This stopper is a Victorian-era glass antique door knob that happened to be produced with a slight amount of cobalt in the silica mixture. These types of glass will turn this purple color when exposed to light over a long period of time. This slight amethyst color gives this stopper an amazing color while keeping the glass-like clarity. This stopper will not fit a Jack Daniel standard bottle but fit beautifully atop this Weller Special Reserve bottle. These types of knobs are rare!