1890 to 1920
The Jugendstil style reminds me of the adage - from ashes to ashes, dust to dust. Early Vienna Regulators were simple, boxy, austere designs. These developed into the elaborate reality of the Altdeutsch and the Baroque, and then returned to the very simple case styles of clocks from the last period of Vienna Regulators, the Jugendstil period. This period corresponds to the German Art Nouveau furniture period.
Jugendstil cases were made of maple, walnut, and various fruitwoods. Many are solid wood (i.e. not veneered) cases. The Jugendstil cases are plain, rectangular with a simple flat design. What they lack in case style they make up with the use of beveled and leaded glass in the doors, and often ornately engraved or embossed dials, weights and bobs. You have to see a Jugendstil clock running to truly appreciate how visually striking the pendulum is, swinging behind the leaded and beveled glass windows. These clocks tend to have steel-backed pendulum bobs, wood pendulum rods, spun-brass bezels, fairly elaborate dial centers and hands, and very well made cases.