According to Pippa,[19] certain characteristics become apparent in a study of the surviving clocks by Bertolla. The tall-case clocks are narrow and range in height from 7-3/4 feet to 10-1/2 feet. The cases had this excessive height in order to obtain the greatest fall for the month and year movements which Bertolla constructed. For the weight assembly, he substituted a drum wound with a key at the point of the driving wheel in place of the customary pulley. The addition of an intermediate wheel augmented the drop of the weight. Bertolla's movements were solidly constructed from well-hammered brass and iron. He favored the recoil anchor escapement in his clocks and the Graham dead-beat anchor escapement with a seconds' pendulum. The escapement was not always placed in the traditional location in the upper center between the plates. Bertolla occasionally displaced the pendulum to one side, to the lower part of the movement or placed it entirely between two other small plates.[20] He utilized every type of striking work, including the music-box cylinder common in the clocks of the Black Forest and the rack and snail. Bertolla most frequently employed the hour strike and _grand sonnerie_. He often used a single hammer on two bells of different sound with the rack and snail. An example of this type is the clock he produced at the age of 80. To achieve the necessary axis of rotation for the hammer, which is perpendicular to the plate when it strikes the hours, it moves to an oblique position and displaces one of the two long pins in an elongated opening. Bertolla's dial plates were generally well executed, with a raised or separate chapter ring applied to a brass or copper plate, such as a copper-plate _repousse_ and gilt with baroque motifs, or upon a smooth brass plate with spandrels of _repousse_ work usually of silver, in relief and attached. The engraving of the chapter rings was excellent. The hands were well executed in steel or perforated bronze, and occasionally of _repousse_ copper; gilt was applied to the hands made of forged steel. [Illustration: Figure 26.--DIAL PLATE of a brass lantern clock made by Bertolla, found in his workshop after his death. (_Courtesy of Museo Nazionale della Scienza e della Tecnica, Milan._)] In the course of time, Bertolla's home workshop passed from one generation to another within the family. Inevitably, it underwent many modifications until the only original part of the building that remained intact from Bertolla's time was his clockshop. [Illustration: Figure 27.--MOVEMENT of a brass lantern clock made by Bertolla. (_Courtesy of Museo Nazionale della Scienza e della Tecnica, Milan._)]